Free, open-source alternatives to Little Snitch

Little Snitch watches outgoing network connections and asks whether to allow or deny each new one, building rules by app, server, port and protocol. Its network monitor shows where apps connect, on a map and over time, and blocklists can be added on top.

The open-source apps below share the core job of surfacing outgoing connections and blocking the ones you do not trust. LuLu alerts you per program and keeps allow or block rules for each one. PureSnitch puts more weight on showing destinations and enforces its rules through the built-in packet filter, which for now applies them to the whole Mac rather than per app.