Stack Overflow
A language-independent collaboratively edited question and answer site for programmers.

Answer Script
Answer Script is a popular question and answer script, it's the best yahoo answers clone script out there. Most of the features of the answer script have been coded using ajax technology. This allows users to be amazed with the instant results and give that cool modern effect. AnswerScript come...
Answers - phpSoftPro
Powerful question and answer script written in PHP, MySQL and jQuery. Main features: Templates are fully customizable with Smarty template engine, unlimited number of categories and subcategories, SEO friendly pages, rating system, comments system, RSS feeds, Facebook signup / signin and mo...
Coordino
Coordino allows you to create a question and answer system for you and your users to enjoy.
Ja2BU
Open source question and answer script written in PHP, MySQL and jQuery. Main features are: SEO friendly url's, private message system, rating system, comments system.
OSQA
OSQA (Open Source Question and Answer) is an open source question-answer system written in Python with Django
Question2Answer
Question2Answer (Q2A) is a popular open source Q&A solution for Q&A communities similar to StackOverflow or Yahoo Answers, currently in use on 5,664 sites in 40 languages. It is built on the standard PHP/MySQL platform, and runs safe and fast.
ScriptFolder - Questions and Answers
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...
Turnkey Yahoo Answers Clone PHP Script
Frontend Users: Register for a Free Account Answer Questions Ask Questions Browse & Search for Answers & Questions Add a small profile image Create you own Watchlist Convenient Google Search Administrator: Control the entire site User Management Category Management Question Manage...