A social Q&A site encourages your online community to share knowledge and helps create content that is very search engine (SEO) friendly. Question2Answer is a free PHP/MySQL solution for social Q&A sites (like Stack Overflow or Stack Exchange) with the following features: - Five minutes (or less!) to install. - Easy styling with CSS themes. - Fast integrated search engine. - Points-based reputation management. - Categories and/or tags (with auto complete). - Email notifications and RSS support. - Voting, comments and follow-on questions. - Simple and secure admin interface. - PHP/MySQL scalable to 1,000,000+ posts. - Built-in user account management, or... - Single sign-on for existing sites.