- Invisible Captcha – Unobtrusive and flexible spam protection based on the honeypot strategy. It also provides a time-sensitive form submission.
- Rakismet – Easy Akismet and TypePad AntiSpam integration for Rails.
- reCAPTCHA – reCaptcha API helpers for ruby apps.
- Voight-Kampff – A Ruby gem that detects bots, spiders, crawlers and replicants.