1. reCAPTCHA is a free security service that protects your websites from spam and abuse.

  2. Akismet is a spam fighting service that protects millions of WordPress sites from comment and contact form spam.

  3. What Does NoMoreCaptchas Do?

  4. Securimage is a script for generating complex images and CAPTCHA codes to protect forms from spam...

  5. The best captcha alternative. Accessible, Mobile-friendly, and Retina-ready! Available for Node.js, PHP, Ruby, Meteor, jQuery, Angular, and vanilla JS.

  6. UniqPin is a free for non-commercial use service which destiny improve ability of interfaces detect...

  7. Confident Technologies provides free CAPTCHA security software called Confident CAPTCHA, a picture...

  8. FeedCaptcha is a new captcha system, easy to integrate and with meaning for your product.

  9. Open source reCAPTCHA alternative

  10. Easy to use - Nothing stupid your visitors have to type before the form submits.

  11. Mollom is a freemium web service to get rid of spam, unwanted content and fake users on your...

  12. Spam protection plugins for Joomla, WordPress, phpBB3, IP.Board, vBulletin and etc.