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

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

  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. Free Caller ID & Call Blocker app that allows mobile users to block phone calls, identify calls, blacklist unwanted callers and much more.

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

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

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

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

  11. Find a person by a name or phone number worldwide for free using Truecaller.

  12. A plugin to make the process of creating a negative captcha in Rails much less painful