Qwench is a PHP/mySQL based StackOverflow clone. Features: Allow users to post questions and answers, points system similar to StackOverflow, ability to post an article as a knowledge-base (for corporates), ability to lock site to registered users only, clean CSS layout, works in all major browsers. Requirements: PHP 4+ and mySQL.
Create an amazing Questions and Answers, responsive website with ScriptFolder- Questions and Answers. It has been designed with latest technology and gathering features from Yahoo! Answers, Ask, Quora, answerbag etc. ScriptFolder- Questions and Answers created SEO friendly, user-friendly and it is light weight to make your sever run smooth and index your site in search engines faster. User friendly admin panel offers you full privilege to manage your site and install take only 10minutes
Shapado is another Stack Overflow-like app written in Ruby on Rails, mongomapper and mongodb. Using this script you can make a Stack Overflow Clone or a Yahoo Answers Clone