diff --git a/crates/komorebi-bar-core/src/lib.rs b/crates/komorebi-bar-core/src/lib.rs
index b65fd141..9088d849 100644
--- a/crates/komorebi-bar-core/src/lib.rs
+++ b/crates/komorebi-bar-core/src/lib.rs
@@ -16,3 +16,5 @@ pub mod config;
 pub mod render;
 
 pub mod widgets;
+
+pub mod platform;
diff --git a/crates/komorebi-bar-core/src/platform.rs b/crates/komorebi-bar-core/src/platform.rs
new file mode 100644
index 00000000..635e5dc3
--- /dev/null
+++ b/crates/komorebi-bar-core/src/platform.rs
@@ -0,0 +1,48 @@
+//! What the widgets need from the operating system and what differs between the bars.
+//!
+//! A shell implements [`BarPlatform`] and calls [`install`] first thing in `main`; the widgets
+//! reach it through [`platform`] when they are built or clicked.
+
+use std::io;
+use std::sync::OnceLock;
+
+/// A tool the bar opens when a widget is clicked.
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub enum SystemTool {
+    /// The task manager (Task Manager, Activity Monitor)
+    TaskManager,
+    /// The operating system's power and battery settings
+    PowerSettings,
+    /// The operating system's network settings
+    NetworkSettings,
+    /// A URL, in the default browser
+    Url(String),
+}
+
+pub trait BarPlatform: Send + Sync {
+    /// Opens a tool; the result is whether it could be started.
+    fn open_system_tool(&self, tool: SystemTool) -> io::Result<()>;
+
+    /// The GitHub API URL that says which release of this platform's komorebi is the latest.
+    fn latest_release_api_url(&self) -> &'static str;
+
+    /// The glyph the date widget shows as its calendar icon.
+    fn calendar_icon(&self) -> &'static str;
+}
+
+static PLATFORM: OnceLock<&'static dyn BarPlatform> = OnceLock::new();
+
+/// Sets the platform of the process. The first call wins; a second one is ignored.
+pub fn install(platform: &'static dyn BarPlatform) {
+    let _ = PLATFORM.set(platform);
+}
+
+/// # Panics
+///
+/// Panics if [`install`] has not been called: a shell must install its platform before it builds
+/// a widget.
+pub fn platform() -> &'static dyn BarPlatform {
+    *PLATFORM
+        .get()
+        .expect("komorebi_bar_core::platform::install must be called first thing in main")
+}
diff --git a/komorebi-bar/src/main.rs b/komorebi-bar/src/main.rs
index 4ca843f5..89b25c77 100644
--- a/komorebi-bar/src/main.rs
+++ b/komorebi-bar/src/main.rs
@@ -1,5 +1,7 @@
 mod bar;
 mod config;
+mod os;
+pub use komorebi_bar_core::platform;
 pub use komorebi_bar_core::render;
 pub use komorebi_bar_core::selected_frame;
 pub use komorebi_bar_core::ui;
@@ -96,6 +98,8 @@ pub enum KomorebiEvent {
 }
 
 fn main() -> color_eyre::Result<()> {
+    komorebi_bar_core::platform::install(&os::WindowsBar);
+
     unsafe { SetProcessDpiAwarenessContext(DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2) }?;
 
     let opts: Opts = Opts::parse();
diff --git a/komorebi-bar/src/os.rs b/komorebi-bar/src/os.rs
new file mode 100644
index 00000000..2fca94c4
--- /dev/null
+++ b/komorebi-bar/src/os.rs
@@ -0,0 +1,29 @@
+use egui_phosphor::regular::CALENDAR_DOTS;
+use komorebi_bar_core::platform::BarPlatform;
+use komorebi_bar_core::platform::SystemTool;
+use std::io;
+use std::process::Command;
+
+pub struct WindowsBar;
+
+impl BarPlatform for WindowsBar {
+    fn open_system_tool(&self, tool: SystemTool) -> io::Result<()> {
+        match tool {
+            SystemTool::TaskManager => Command::new("cmd.exe").args(["/C", "taskmgr.exe"]).spawn(),
+            SystemTool::PowerSettings => Command::new("cmd.exe")
+                .args(["/C", "start", "ms-settings:batterysaver"])
+                .spawn(),
+            SystemTool::NetworkSettings => Command::new("cmd.exe").args(["/C", "ncpa"]).spawn(),
+            SystemTool::Url(url) => Command::new("explorer.exe").args([url]).spawn(),
+        }
+        .map(|_| ())
+    }
+
+    fn latest_release_api_url(&self) -> &'static str {
+        "https://api.github.com/repos/LGUG2Z/komorebi/releases/latest"
+    }
+
+    fn calendar_icon(&self) -> &'static str {
+        CALENDAR_DOTS
+    }
+}
diff --git a/komorebi-for-mac/komorebi-bar/src/main.rs b/komorebi-for-mac/komorebi-bar/src/main.rs
index 857092c2..c08f444c 100644
--- a/komorebi-for-mac/komorebi-bar/src/main.rs
+++ b/komorebi-for-mac/komorebi-bar/src/main.rs
@@ -1,5 +1,7 @@
 mod bar;
 mod config;
+mod os;
+pub use komorebi_bar_core::platform;
 pub use komorebi_bar_core::render;
 pub use komorebi_bar_core::selected_frame;
 pub use komorebi_bar_core::ui;
@@ -63,6 +65,8 @@ pub enum KomorebiEvent {
 }
 
 fn main() -> eyre::Result<()> {
+    komorebi_bar_core::platform::install(&os::MacBar);
+
     let opts: Opts = Opts::parse();
 
     #[cfg(feature = "schemars")]
diff --git a/komorebi-for-mac/komorebi-bar/src/os.rs b/komorebi-for-mac/komorebi-bar/src/os.rs
new file mode 100644
index 00000000..c3df076a
--- /dev/null
+++ b/komorebi-for-mac/komorebi-bar/src/os.rs
@@ -0,0 +1,35 @@
+use egui_phosphor::regular::CALENDAR;
+use komorebi_bar_core::platform::BarPlatform;
+use komorebi_bar_core::platform::SystemTool;
+use std::io;
+use std::process::Command;
+
+pub struct MacBar;
+
+impl BarPlatform for MacBar {
+    fn open_system_tool(&self, tool: SystemTool) -> io::Result<()> {
+        match tool {
+            SystemTool::TaskManager => Command::new("open")
+                .args(["-a", "Activity Monitor"])
+                .spawn(),
+            // cmd.exe does not exist on macOS: this is what the battery widget does today
+            SystemTool::PowerSettings => Command::new("cmd.exe")
+                .args(["/C", "start", "ms-settings:batterysaver"])
+                .spawn(),
+            SystemTool::NetworkSettings => Command::new("open")
+                .args(["x-apple.systempreferences:com.apple.Network-Settings.extension"])
+                .spawn(),
+            // explorer.exe does not exist on macOS: this is what the update widget does today
+            SystemTool::Url(url) => Command::new("explorer.exe").args([url]).spawn(),
+        }
+        .map(|_| ())
+    }
+
+    fn latest_release_api_url(&self) -> &'static str {
+        "https://api.github.com/repos/LGUG2Z/komorebi-for-mac/releases/latest"
+    }
+
+    fn calendar_icon(&self) -> &'static str {
+        CALENDAR
+    }
+}