Playbit Runtime - Personal-Scale Software Platform
Playbit is a new software platform for building "joyful personal-scale software" - programs by you, for you, and for the people in your life.
Key Concepts:
- Personal-scale software: Apps for friends that actually all can run - avoiding the web as the only option
- Cross-platform vision: Same app runs on macOS, Windows, Linux, iOS, Android, and web
- Minimal ABI-stable syscall interface: Like an OS kernel living inside a host environment
- Capabilities-first: Everything is an object behind a handle with access rights
- Nested sandboxes: Handles are thread-local, can be duplicated with fewer rights
The runtime uses a narrow ABI where guest code enters through pb_thread and communicates via pb_syscall. Each call carries an opcode, subject handle, and integer arguments - keeping the boundary stable and inspectable.
Interesting design decisions include poll-based async (no callbacks pushed into guest code), thread-local handles for security, and clear fault boundaries with message passing between threads.