Keystone Desktop

A desktop application framework. Three processes — a C# host, a Bun runtime, and a WebKit renderer — form a triangle with full bidirectional communication across every edge. Build your UI in web tech, your backend in TypeScript, and your native layer in C# with direct GPU access. Or use any subset.

              Browser (WebKit)
          ╱                     ╲
     invoke()              invokeBun()
     fetch("/api/…")       query() / send()
     push                  subscribe()
          ╲                     ╱
    C#  Host ◄── stdin/stdout ──► Bun
    (.NET 10)     (NDJSON)      (TypeScript)

https://discord.gg/d2GVrZJda7

What you can build

Web-only — TypeScript UI + Bun services, zero C#. Declare windows in keystone.json, implement them as web components using any framework. Built-in APIs cover file dialogs, window management, clipboard, shell integration, and more.

Hybrid — Web UI for your interface, C# for platform integration or GPU rendering. A single window can composite GPU/Skia content and WebKit panels together.

Native-only — Pure C# with GPU/Skia rendering and Flex layout via Taffy. No browser overhead. For visualization tools, real-time graphics, or performance-critical workloads.

All three modes compose freely in a single app.

Why these choices

C# over Rust, Go, or Swift — .NET 10 has mature platform bindings across macOS, Linux, and Windows, first-class async, and a plugin system (AssemblyLoadContext) that makes hot-reload genuinely good. Swift would mean no Linux/Windows story. Rust would mean writing platform bindings from scratch. C# is the pragmatic choice for a framework that needs to be native-capable and developer-friendly across platforms.

Bun over Node or Deno — Bun's built-in bundler eliminates a separate bundler process entirely. The TypeScript → browser-ready JS pipeline runs inside Bun with zero configuration. Startup time matters for subprocess restart recovery, and Bun starts in milliseconds.

Separate Bun process — Process isolation means a JS crash doesn't kill the C# host. But the deeper reason is that Bun makes the TypeScript layer fully self-contained — bundler, package manager, runtime, and test runner in one binary. No webpack, no vite, no esbuild config.

WebKit slots instead of a full-window WebView — The GPU/Skia layer renders anywhere a web component doesn't occupy. This enables hybrid windows: native chrome, native data visualization, or native toolbars composited with web UI panels in one window. A full-window WebView would surrender the entire pixel budget to the browser.

Flexbox via Rust FFI — Taffy is a production-quality flexbox/grid implementation. Layout input goes in, computed rects come out. Writing a flexbox engine in C# would be a significant project for no real gain.

Platform stack

Quick start

python3 tools/create-app.py my-app
cd my-app
python3 build.py --run

Requirements: .NET 10 SDK, Bun, Rust toolchain, and platform dependencies (macOS 15+ Apple Silicon, or GTK4 + WebKitGTK on Linux, or Windows 10 1903+).

Documentation

License

MIT