HumanDetector is a friendly logic captcha for Rails the doesn't require any external system dependency (e.g. external captcha API connections). It uses a simple question that any 7 or more years old human can understand, but that a spambot will not be able to answer. This Gem supports Ruby v1.9.2...

A simple and custom captcha for Rails3.

A simple CAPTCHA implementation for Rails 5+ based on RMagick.

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

Death by Captcha Ruby implementation (HTTP API)

RedisCaptcha provides simple captcha that can be read by human.

Rails mountable engine, that provides captcha support

Captcha form Jike API

A simple image captcha gem

MVC based Math, Logic Captcha

Simple captcha based on plain text questions.

simple stupid captcha

adds audio support to simple captcha

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

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

Simple Audio Extension to Simple Captcha

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

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.

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.

Captcha Client for YunPian.com