reCAPTCHA was too much for us, so we created this. Simplest captcha ever.

SimpleCaptcha is available to be used with Rails 3 + 4 or above and also it provides the backward compatibility with previous versions of Rails.

Simple gem to add captcha or negative captcha to your Rails 3 application

anti-captcha is a Ruby library for recognize captcha on anti-captcha.com

A captcha solver (only for easy ones) gem

DeathByCaptcha allows you to solve captchas with manual labor

A Google-style captcha for enterprise Rails apps

A Google-style captcha for enterprise Rails apps

A captcha verification approach for Rails apps, directly integrated into ActiveRecord’s validation mechanism and providing helpers for ActionController and ActionView.

SimpleCaptcha is the simplest and a robust captcha. Its implementation requires adding up a single line in views and in controllers/models. SimpleCaptcha is available to be used with Rails2.0 or above and also it provides the backward compatibility with previous versions of Rails.

ReCaptcha implements view helpers to generate ReCaptcha code, with the noscript counterpart, required methods that interface with the HTTP API for captcha verification, a DSL to generate a before_filter and the code to implement AJAX captcha validation.

Simple reverse captcha solution that consist in create a hidden field that should be always empty.

A simple and custom captcha for Rails3.

generate captcha by dalli,use the memcache

Simple Audio Extension to Simple Captcha

It's a Rails Captcha Engine for Rails 3 applications.

Death by Captcha Ruby implementation (HTTP API)

MVC based Math, Logic Captcha

Simple lib to generate a math_captcha to prevent spammers in form. Supports localization.

RMagickCaptcha is a gem that implements captcha for using in Rails application.