Question2Answer (Q2A) is a popular free open source Q&A platform for PHP/MySQL, used by over 22,000 sites in 40 languages.

• Asking and answering questions (duh!)
• Voting, comments, best answer selection, follow-on and closed questions.
• Complete user management including points-based reputation management.
• Create experts, editors, moderators and admins.
• Fast integrated search engine, plus checking for similar questions when asking.
• Categories (up to 4 levels deep) and/or tagging.
• Easy styling with CSS themes.
• Supports translation into any language.
• Custom sidebar, widgets, pages and links.
• SEO features such as neat URLs, microformats and XML Sitemaps.
• RSS, email notifications and personal news feeds.
• User avatars (or Gravatar) and custom fields.
• Private messages and public wall posts.
• Log in via Facebook or others (using plugins).
• Out-of-the-box WordPress 3+ integration.
• Out-of-the-box Joomla! 3.0+ integration (in conjunction with a Joomla! extension).
• Custom single sign-on support for other sites.
• PHP/MySQL scalable to millions of users and posts.
• Safe from XSS, CSRF and SQL injection attacks.
• Beat spam with captchas, rate-limiting, moderation and/or flagging.
• Block users, IP addresses, and censor words

Q2A also features an extensive plugin system:

• Modify the HTML output for a page with layers.
• Add custom pages to a Q2A site with page modules.
• Add extra content in various places with widget modules.
• Allow login via an external identity provider such as Facebook with login modules.
• Integrate WYSIWYG or other text editors with editor/viewer modules.
• Do something when certain actions take place with event modules.
• Validate and/or modify many types of user input with filter modules.
• Implement a custom search engine with search modules.
• Add extra spam protection with captcha modules.
• Extend many core Q2A functions using function overrides.

Q2A themes, plugins and language files created by other members are available here.

Question2Answer is open source and we welcome contributions! The collaborative development process is being managed by Scott Vivian. Please read the contributing page for more information on how to get involved. We also have an active community where you can ask for help and discuss Q2A with other members.

Official releases can be found either on the Q2A website or via the Releases tab on GitHub.