A simple and custom captcha for Rails3.

Death by Captcha Ruby implementation (HTTP API)

RedisCaptcha provides simple captcha that can be read by human.

Simple Audio Extension to Simple Captcha

Captcha form Jike API

Gem that uses RuCaptcha API to solver any type of captcha

adds audio support to simple captcha

A simple image captcha gem

generate captcha by dalli,use the memcache

MVC based Math, Logic Captcha

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

Rack middleware Captcha verification using Recaptcha API.

BrainBuster - a logic captcha for Rails

Despamilator is a plugin based spam detector designed for use on your web forms borne out of two annoyances: Spam being submitted in my web forms and CAPTCHAS being intrusive. Despamilator will apply some commonly used heuristics from the world of anti-spam to help you decide whether your users are human or machine.

ActsAsTextcaptcha provides spam protection for Rails models with text-based logic question captchas. Questions are fetched from Rob Tuley's textcaptcha.com They can be solved easily by humans but are tough for robots to crack.

RubyGem package for visualCaptcha's backend service

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

.

Arithmetic Captcha

Drop in feedback engine with customizable fields, and captcha available