Numbat

Perplexity's free open-source tool that watches what AI agents do on a computer and can stop risky actions before they run.

Watches agent activity on the machine itself, so it covers desktop apps, command-line tools, coding-editor agents, and gateway agents rather than one product
Ships with 52 detection rules across 11 categories of behavior, including privilege escalation, secrets being copied out, and moving between systems
Flags sequences of actions, not only single ones, such as reading a secret and then sending data out
Reconstructs what happened after the fact from the logs and session transcripts an agent already left behind
One program for macOS, Linux, and Windows, free and open source on GitHub under the Apache 2.0 license