mCaptcha is a privacy-focused and reliable solution that does not track or profile users. It is designed to work seamlessly even for users behind NATs, as it does not rely on IP addresses for rate limiting. The unique aspect of mCaptcha is its silent user experience, ensuring that users are not bothered by annoying images or assisting Big Brothers with their Machine Learning endeavors. The robust PoW-based solution employed by mCaptcha makes it more difficult and expensive for attackers to target your site. The client libraries are licensed using proprietary-friendly free software licenses, while the core remains AGPL’d. mCaptcha also offers compatibility with popular captcha solutions like reCAPTCHA and hCaptcha, making it an easy drop-in replacement.
https://mcaptcha.org/