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

API to interact with BrandCAPTCHA http://www.pontamedia.com/en/brandcaptcha/

Simple negative captcha for Rails

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

A smart captcha library

TrustCaptcha – Privacy-first CAPTCHA solution for Ruby. GDPR-compliant, bot protection made in Europe.

Easy to use classical captcha for Rails apps

Description of TinyCaptcha.

To help with keep the bots at bay this gem helps you easily add honeypots to forms and/or obfuscate your form field names

Simple negative captcha for Rails

Metabypass | Ruby-based easy implementation for solving any type of captcha by Metabypass

This library can help you create a captcha in your terminal application, which may be damaged by a large influx of requests.

you will get arithmatic sum with answer you just have to compare with ur user in controller

Integrate the AreYouAHuman.com CAPTCHA alternative human verification into your Ruby/Rails application

Generates and verifies ascii art captcha.

My version of SimpleCaptcha

Form protection with simple captcha calculations.