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.

Rails mountable engine, that provides captcha support

Gem that uses RuCaptcha API to solver any type of captcha

MVC based Math, Logic Captcha

This is a Captcha gem for ruby. It drawing captcha image with C code so it no dependencies.

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

Simple captcha based on plain text questions.

Use Turnstile by Cloudflare to perform captcha validation in your Rails app

A simple and custom captcha for Rails3.

generate captcha by dalli,use the memcache

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

Captcha Gem for Rails, which generates captcha image by Rust.

Death by Captcha Ruby implementation (HTTP API)

RedisCaptcha provides simple captcha that can be read by human.

A simple image captcha gem

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

Simple, easy captcha for Sinatra

adds audio support to simple captcha

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

Simple Audio Extension to Simple Captcha