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.

Drop in feedback engine with customizable fields, and captcha available

ZeroCaptcha allows companies to solve captchas with artificial intelligence software, which is faster than humans and very accurate

A Google-style captcha for enterprise Rails apps

A Google-style captcha for enterprise Rails apps

Arithmetic Captcha

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

A Rails captcha gem that attempts to determine whether or not a user is human.

Antigate (Decode captcha service) wrapper for Ruby

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

Easy to use classical captcha for Rails apps

Ruby package for easy integration with the API of 2captcha captcha solving service to bypass recaptcha, hcaptcha, funcaptcha, geetest and solve any other captchas.

Simple Audio Extension to Simple Captcha

Generates Text Catpchas, that are 'nice' by my own personal definition!

AntiCaptcha api ruby wrapper

A captcha that uses images instead of garbled text

A simple way to add zero friction captchas to Rails forms

Captcha library which uses imagemagick to create captchas

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 and fast image captcha generator that uses opencv and memcached.