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

A simple and custom captcha for Rails3.

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

Simple, easy captcha for Sinatra

Captcha form Jike API

simple stupid captcha

adds audio support to simple captcha

Captcha Client for YunPian.com

MVC based Math, Logic Captcha

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

Simple captcha based on plain text questions.

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

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

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...

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.

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

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

DeathByCaptcha allows you to solve captchas with manual labor

Rack middleware Captcha verification using Recaptcha API.

BrainBuster - a logic captcha for Rails