diff --git a/Cargo.lock b/Cargo.lock
index f02baf5..5128401 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -756,6 +756,18 @@ dependencies = [
  "typenum",
 ]
 
+[[package]]
+name = "dimensioned"
+version = "0.8.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a0b0a86c5d31c93238ff4b694fa31f3acdf67440770dc314c57d90e433914397"
+dependencies = [
+ "generic-array 0.14.7",
+ "num-traits",
+ "serde 1.0.188",
+ "typenum",
+]
+
 [[package]]
 name = "displaydoc"
 version = "0.2.4"
@@ -807,7 +819,7 @@ version = "0.6.0"
 dependencies = [
  "chrono",
  "chrono-tz",
- "dimensioned",
+ "dimensioned 0.7.0",
  "serde 1.0.188",
  "serde_derive",
  "serde_json",
@@ -960,6 +972,18 @@ version = "1.2.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "8fcfdc7a0362c9f4444381a9e697c79d435fe65b52a37466fc2c1184cee9edc6"
 
+[[package]]
+name = "fitnesstrax"
+version = "0.1.0"
+dependencies = [
+ "gio",
+ "glib",
+ "glib-build-tools 0.18.0",
+ "gtk4",
+ "libadwaita",
+ "tokio",
+]
+
 [[package]]
 name = "flate2"
 version = "1.0.27"
@@ -1104,6 +1128,18 @@ dependencies = [
  "syn 2.0.37",
 ]
 
+[[package]]
+name = "ft-core"
+version = "0.1.0"
+dependencies = [
+ "chrono",
+ "chrono-tz",
+ "dimensioned 0.8.0",
+ "emseries",
+ "serde 1.0.188",
+ "tempfile",
+]
+
 [[package]]
 name = "fuchsia-cprng"
 version = "0.1.1"
diff --git a/Cargo.toml b/Cargo.toml
index 1957e1d..73f671e 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -10,6 +10,8 @@ members = [
     "dashboard",
     "emseries",
     "file-service",
+    "fitnesstrax/core",
+    "fitnesstrax/app",
     "fluent-ergonomics",
     "geo-types",
     "gm-control-panel",
diff --git a/build.sh b/build.sh
index dcaed56..8311bd5 100755
--- a/build.sh
+++ b/build.sh
@@ -11,6 +11,7 @@ RUST_ALL_TARGETS=(
     "dashboard"
     "emseries"
     "file-service"
+    "fitnesstrax"
     "fluent-ergonomics"
     "geo-types"
     "gm-control-panel"
diff --git a/emseries/src/series.rs b/emseries/src/series.rs
index 71e089f..98f0cb1 100644
--- a/emseries/src/series.rs
+++ b/emseries/src/series.rs
@@ -42,7 +42,7 @@ where
 {
     /// Open a time series database at the specified path. `path` is the full path and filename for
     /// the database.
-    pub fn open(path: &str) -> Result<Series<T>, EmseriesReadError> {
+    pub fn open<P: AsRef<std::path::Path>>(path: P) -> Result<Series<T>, EmseriesReadError> {
         let f = OpenOptions::new()
             .read(true)
             .append(true)
diff --git a/emseries/tests/test_io.rs b/emseries/tests/test_io.rs
index c599369..3f26f16 100644
--- a/emseries/tests/test_io.rs
+++ b/emseries/tests/test_io.rs
@@ -99,8 +99,8 @@ mod test {
     {
         let tmp_file = tempfile::NamedTempFile::new().expect("temporary path created");
         let tmp_path = tmp_file.into_temp_path();
-        let ts: Series<BikeTrip> = Series::open(&tmp_path.to_string_lossy())
-            .expect("the time series should open correctly");
+        let ts: Series<BikeTrip> =
+            Series::open(&tmp_path).expect("the time series should open correctly");
         test(ts);
     }
 
@@ -136,8 +136,8 @@ mod test {
     pub fn can_search_for_an_entry_with_exact_time() {
         run_test(|path| {
             let trips = mk_trips();
-            let mut ts: Series<BikeTrip> = Series::open(&path.to_string_lossy())
-                .expect("expect the time series to open correctly");
+            let mut ts: Series<BikeTrip> =
+                Series::open(&path).expect("expect the time series to open correctly");
 
             for trip in &trips[0..=4] {
                 ts.put(trip.clone()).expect("expect a successful put");
@@ -157,8 +157,8 @@ mod test {
     pub fn can_get_entries_in_time_range() {
         run_test(|path| {
             let trips = mk_trips();
-            let mut ts: Series<BikeTrip> = Series::open(&path.to_string_lossy())
-                .expect("expect the time series to open correctly");
+            let mut ts: Series<BikeTrip> =
+                Series::open(&path).expect("expect the time series to open correctly");
 
             for trip in &trips[0..=4] {
                 ts.put(trip.clone()).expect("expect a successful put");
@@ -186,8 +186,8 @@ mod test {
             let trips = mk_trips();
 
             {
-                let mut ts: Series<BikeTrip> = Series::open(&path.to_string_lossy())
-                    .expect("expect the time series to open correctly");
+                let mut ts: Series<BikeTrip> =
+                    Series::open(&path).expect("expect the time series to open correctly");
 
                 for trip in &trips[0..=4] {
                     ts.put(trip.clone()).expect("expect a successful put");
@@ -195,8 +195,8 @@ mod test {
             }
 
             {
-                let ts: Series<BikeTrip> = Series::open(&path.to_string_lossy())
-                    .expect("expect the time series to open correctly");
+                let ts: Series<BikeTrip> =
+                    Series::open(&path).expect("expect the time series to open correctly");
                 let v: Vec<(&UniqueId, &BikeTrip)> = ts.search_sorted(
                     time_range(
                         DateTimeTz(UTC.with_ymd_and_hms(2011, 10, 31, 0, 0, 0).unwrap()).into(),
@@ -220,8 +220,8 @@ mod test {
             let trips = mk_trips();
 
             {
-                let mut ts: Series<BikeTrip> = Series::open(&path.to_string_lossy())
-                    .expect("expect the time series to open correctly");
+                let mut ts: Series<BikeTrip> =
+                    Series::open(&path).expect("expect the time series to open correctly");
 
                 for trip in &trips[0..=2] {
                     ts.put(trip.clone()).expect("expect a successful put");
@@ -229,8 +229,8 @@ mod test {
             }
 
             {
-                let mut ts: Series<BikeTrip> = Series::open(&path.to_string_lossy())
-                    .expect("expect the time series to open correctly");
+                let mut ts: Series<BikeTrip> =
+                    Series::open(&path).expect("expect the time series to open correctly");
                 let v: Vec<(&UniqueId, &BikeTrip)> = ts.search_sorted(
                     time_range(
                         DateTimeTz(UTC.with_ymd_and_hms(2011, 10, 31, 0, 0, 0).unwrap()).into(),
@@ -248,8 +248,8 @@ mod test {
             }
 
             {
-                let ts: Series<BikeTrip> = Series::open(&path.to_string_lossy())
-                    .expect("expect the time series to open correctly");
+                let ts: Series<BikeTrip> =
+                    Series::open(&path).expect("expect the time series to open correctly");
                 let v: Vec<(&UniqueId, &BikeTrip)> = ts.search_sorted(
                     time_range(
                         DateTimeTz(UTC.with_ymd_and_hms(2011, 10, 31, 0, 0, 0).unwrap()).into(),
@@ -273,8 +273,8 @@ mod test {
         run_test(|path| {
             let trips = mk_trips();
 
-            let mut ts: Series<BikeTrip> = Series::open(&path.to_string_lossy())
-                .expect("expect the time series to open correctly");
+            let mut ts: Series<BikeTrip> =
+                Series::open(&path).expect("expect the time series to open correctly");
 
             ts.put(trips[0].clone()).expect("expect a successful put");
             ts.put(trips[1].clone()).expect("expect a successful put");
@@ -310,8 +310,8 @@ mod test {
             let trips = mk_trips();
 
             {
-                let mut ts: Series<BikeTrip> = Series::open(&path.to_string_lossy())
-                    .expect("expect the time series to open correctly");
+                let mut ts: Series<BikeTrip> =
+                    Series::open(&path).expect("expect the time series to open correctly");
 
                 ts.put(trips[0].clone()).expect("expect a successful put");
                 ts.put(trips[1].clone()).expect("expect a successful put");
@@ -327,8 +327,8 @@ mod test {
             }
 
             {
-                let ts: Series<BikeTrip> = Series::open(&path.to_string_lossy())
-                    .expect("expect the time series to open correctly");
+                let ts: Series<BikeTrip> =
+                    Series::open(&path).expect("expect the time series to open correctly");
 
                 let trips: Vec<(&UniqueId, &BikeTrip)> = ts.records().collect();
                 assert_eq!(trips.len(), 3);
@@ -356,8 +356,8 @@ mod test {
             let trips = mk_trips();
 
             {
-                let mut ts: Series<BikeTrip> = Series::open(&path.to_string_lossy())
-                    .expect("expect the time series to open correctly");
+                let mut ts: Series<BikeTrip> =
+                    Series::open(&path).expect("expect the time series to open correctly");
                 let trip_id = ts.put(trips[0].clone()).expect("expect a successful put");
                 ts.put(trips[1].clone()).expect("expect a successful put");
                 ts.put(trips[2].clone()).expect("expect a successful put");
@@ -368,8 +368,8 @@ mod test {
             }
 
             {
-                let ts: Series<BikeTrip> = Series::open(&path.to_string_lossy())
-                    .expect("expect the time series to open correctly");
+                let ts: Series<BikeTrip> =
+                    Series::open(&path).expect("expect the time series to open correctly");
                 let recs: Vec<(&UniqueId, &BikeTrip)> = ts.records().collect();
                 assert_eq!(recs.len(), 2);
             }
diff --git a/fitnesstrax/app/Cargo.toml b/fitnesstrax/app/Cargo.toml
new file mode 100644
index 0000000..4692329
--- /dev/null
+++ b/fitnesstrax/app/Cargo.toml
@@ -0,0 +1,17 @@
+[package]
+name = "fitnesstrax"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+adw             = { version = "0.5", package = "libadwaita", features = [ "v1_2" ] }
+gio             = { version = "0.18" }
+glib            = { version = "0.18" }
+gtk             = { version = "0.7", package = "gtk4", features = [ "v4_8" ] }
+tokio           = { version = "1.34", features = [ "full" ] }
+
+[build-dependencies]
+glib-build-tools = "0.18"
+
diff --git a/fitnesstrax/app/src/main.rs b/fitnesstrax/app/src/main.rs
new file mode 100644
index 0000000..3204d89
--- /dev/null
+++ b/fitnesstrax/app/src/main.rs
@@ -0,0 +1,38 @@
+use fitnesstrax;
+use gtk::prelude::*;
+use std::env;
+
+struct AppState {}
+
+struct AppWindow {
+    window: adw::ApplicationWindow,
+}
+
+fn main() {
+    println!("Hello, world!");
+
+    let app = adw::Application::builder()
+        .application_id("com.luminescent-dreams.fitnesstrax")
+        .resource_base_path("/com/luminescent-dreams/fitnesstrax")
+        .build();
+
+    /*
+    let runtime = tokio::runtime::Builder::new_multi_thread()
+        .enable_all()
+        .build()
+        .unwrap();
+        */
+
+    let app = adw::Application::builder()
+        .application_id("com.luminescent-dreams.fitnesstrax")
+        .resource_base_path("/com/luminescent-dreams/fitnesstrax")
+        .build();
+
+    app.connect_activate(move |app| {
+        let window = adw::ApplicationWindow::new(app);
+        window.present();
+    });
+
+    let args: Vec<String> = env::args().collect();
+    ApplicationExtManual::run_with_args(&app, &args);
+}
diff --git a/fitnesstrax/core/Cargo.toml b/fitnesstrax/core/Cargo.toml
new file mode 100644
index 0000000..520b69c
--- /dev/null
+++ b/fitnesstrax/core/Cargo.toml
@@ -0,0 +1,18 @@
+[package]
+name = "ft-core"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+chrono          = { version = "0.4" }
+chrono-tz       = { version = "0.8" }
+dimensioned     = { version = "0.8", features = [ "serde" ] }
+emseries        = { path = "../../emseries" }
+serde           = { version = "1", features = [ "derive" ] }
+
+[dev-dependencies]
+tempfile        = "*"
+
+
diff --git a/fitnesstrax/core/src/legacy.rs b/fitnesstrax/core/src/legacy.rs
new file mode 100644
index 0000000..0a79713
--- /dev/null
+++ b/fitnesstrax/core/src/legacy.rs
@@ -0,0 +1,24 @@
+use crate::types;
+
+#[cfg(test)]
+mod test {
+    #[test]
+    fn read_a_legacy_set_rep_record() {
+        unimplemented!()
+    }
+
+    #[test]
+    fn read_a_legacy_steps_record() {
+        unimplemented!()
+    }
+
+    #[test]
+    fn read_a_legacy_time_distance_record() {
+        unimplemented!()
+    }
+
+    #[test]
+    fn read_a_legacy_weight_record() {
+        unimplemented!()
+    }
+}
diff --git a/fitnesstrax/core/src/lib.rs b/fitnesstrax/core/src/lib.rs
new file mode 100644
index 0000000..b591639
--- /dev/null
+++ b/fitnesstrax/core/src/lib.rs
@@ -0,0 +1,6 @@
+use chrono::NaiveDate;
+use dimensioned::si;
+use emseries::DateTimeTz;
+
+mod legacy;
+mod types;
diff --git a/fitnesstrax/core/src/types.rs b/fitnesstrax/core/src/types.rs
new file mode 100644
index 0000000..4c332d1
--- /dev/null
+++ b/fitnesstrax/core/src/types.rs
@@ -0,0 +1,106 @@
+use chrono::NaiveDate;
+use dimensioned::si;
+use emseries::{DateTimeTz, Recordable, Timestamp};
+use serde::{Deserialize, Serialize};
+
+/// SetRep represents workouts like pushups or situps, which involve doing a "set" of a number of
+/// actions, resting, and then doing another set.
+pub struct SetRep {
+    /// I assume that a set/rep workout is only done once in a day.
+    date: NaiveDate,
+    /// Each set entry represents the number of times that the action was performed in a set. So, a
+    /// pushup workout that involved five sets would have five entries. Each entry would be x
+    /// number of pushups. A viable workout would be something like [6, 6, 4, 4, 5].
+    sets: Vec<u32>,
+    comments: Option<String>,
+}
+
+/// The number of steps one takes in a single day.
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
+pub struct Steps {
+    date: NaiveDate,
+    count: u32,
+}
+
+/// TimeDistance represents workouts characterized by a duration and a distance travelled. These
+/// sorts of workouts can occur many times a day, depending on how one records things. I might
+/// record a single 30-km workout if I go on a long-distanec ride. Or I might record multiple 5km
+/// workouts if I am out running errands. Distance and Duration are both optional because different
+/// people have different priorities and may choose to measure different things.
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
+pub struct TimeDistance {
+    /// The precise time (and the relevant timezone) of the workout. One of the edge cases that I
+    /// account for is that a ride which occurred at 11pm in one timezone would then count as 1am
+    /// if one moved two timezones to the east. This is kind of nonsensical from a human
+    /// perspective, so the DateTimeTz keeps track of the precise time in UTC, but also the
+    /// timezone in which the event was recorded.
+    datetime: DateTimeTz,
+    /// The distance travelled. This is optional because such a workout makes sense even without
+    /// the distance.
+    distance: Option<si::Meter<f64>>,
+    /// The duration of the workout, which is also optional. Some people may keep track of the
+    /// amount of distance travelled without tracking the duration.
+    duration: Option<si::Second<f64>>,
+    comments: Option<String>,
+}
+
+/// A singular daily weight measurement. Weight changes slowly enough that it seems unlikely to
+/// need to track more than a single weight in a day.
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
+pub struct Weight {
+    date: NaiveDate,
+    weight: si::Kilogram<f64>,
+}
+
+/// The unified data structure for all records that are part of the app.
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
+pub enum TraxRecord {
+    BikeRide(TimeDistance),
+    Row(TimeDistance),
+    Run(TimeDistance),
+    Steps(Steps),
+    Swim(TimeDistance),
+    Walk(TimeDistance),
+    Weight(Weight),
+}
+
+impl Recordable for TraxRecord {
+    fn timestamp(&self) -> Timestamp {
+        match self {
+            TraxRecord::BikeRide(rec) => Timestamp::DateTime(rec.datetime.clone()),
+            TraxRecord::Row(rec) => Timestamp::DateTime(rec.datetime.clone()),
+            TraxRecord::Run(rec) => Timestamp::DateTime(rec.datetime.clone()),
+            TraxRecord::Steps(rec) => Timestamp::Date(rec.date),
+            TraxRecord::Swim(rec) => Timestamp::DateTime(rec.datetime.clone()),
+            TraxRecord::Walk(rec) => Timestamp::DateTime(rec.datetime.clone()),
+            TraxRecord::Weight(rec) => Timestamp::Date(rec.date),
+        }
+    }
+
+    fn tags(&self) -> Vec<String> {
+        vec![]
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+    use emseries::Series;
+
+    #[test]
+    fn can_record_records() {
+        let file = tempfile::NamedTempFile::new().expect("a temporary file");
+        let path = file.into_temp_path();
+        let mut series: Series<TraxRecord> = Series::open(&path).unwrap();
+
+        let record = TraxRecord::Steps(Steps {
+            date: NaiveDate::from_ymd_opt(2023, 1, 1).unwrap(),
+            count: 1000,
+        });
+
+        let id = series.put(record.clone()).unwrap();
+
+        let record_ = series.get(&id).unwrap();
+        assert_eq!(record_, record);
+    }
+}