Cap

An open-source CAPTCHA service that keeps bots out of forms and sign-up flows. Rather than image puzzles, Cap runs a small widget in the background that pairs proof-of-work hashing with a generated JavaScript challenge inspecting the browser environment, so a request must pass two independent layers before it is accepted.

It suits teams replacing reCAPTCHA or hCaptcha on registration, login, password reset and comment forms who want to stop sending visitor data to an external vendor.

Running Cap yourself keeps challenge data on your own server, with no telemetry, quotas or per-request fees; the widget can be styled to match your site.