littlesnitch-linux

Objective Development open-sourced the eBPF networking components behind Little Snitch, their macOS firewall, and brought them to Linux. This gives you kernel-level control over outbound network connections: monitor what your system talks to and block what you don't want.

Setup is developer-grade. You need Rust, clang, and bpf-linker to build from source. Traffic filtering works through plain text blocklists (domains and hosts), and the web UI is minimal. This is not a consumer product yet. It's the engine room, published for people who know what eBPF is and why they want it.

Security-conscious developers and sysadmins running Linux workstations are the audience. Anyone who wants kernel-level visibility into every outbound connection, and is comfortable building Rust projects, will feel right at home.

The catch: GPL-2.0 covers the open source parts, but some components remain proprietary. No GUI to speak of, manual blocklist management, and the build process will filter out anyone who isn't already comfortable in a terminal.