mCaptcha

mCaptcha takes the same privacy-respecting approach as ALTCHA and aims it squarely at flood protection: it does not use a visitor’s IP address to rate-limit and it builds no profile, while every check stays on infrastructure you control. For a webmaster who already self-hosts and is comfortable on the command line, the lightweight Rust backend is a clean fit. The catch is twofold. The ecosystem is smaller than the bigger names, so you lean on the project’s own docs, and there is no managed tier, so you own the deployment and its upkeep. Pick it if you run your own stack and want spam control with zero visitor tracking. Skip it if you need a drop-in widget someone else hosts.