New Project idea: fcage

[ata-sesli]

fcage — Native process isolation without VMs

I’m considering building a cross-platform CLI tool called fcage.

The name is inspired by the Faraday cage: the idea is to put a process inside a controlled boundary and limit what can cross it.

The project came from a simple habit I want to have: whenever I’m unsure about a command, installer, package, binary, development tool, or agent, I should be able to prefix it with fcage instead of reaching for a VM.

For example:

fcage npm install
fcage ./unknown-binary
fcage --observe ./installer
fcage --no-network some-command

The tool would run processes natively while controlling things such as:

-filesystem read access
-filesystem write access
-process execution and spawning
-network access
-environment exposure
-attempted actions for observation and auditing

The goal is not to build another Docker or container platform. There would be no images, orchestration, Compose-like features, or VM layer.

Instead, fcage would provide a unified permission model over native OS sandboxing mechanisms. The initial targets would be macOS and Linux, using Seatbelt / sandbox-exec on macOS and bubblewrap + seccomp on Linux. Windows can also be a target afterwards.

The most important part of the idea is zero-friction usage: fcage should already provide sensible isolation without requiring the user to design a sandbox policy every time.

Observation could later become a major part of the tool as well, showing what a process tried to read, write, execute, or connect to.

The current direction is to implement the CLI in Zig and keep the project intentionally small and focused.

I’d like to hear thoughts about the idea, possible use cases, threat-model considerations, and what the default isolation policy should look like.

All contributions are welcome.