Stack Overflow
Q&A for professional and enthusiast programmers
Game Development
Q&A for professional and independent game developers
Science Fiction & Fantasy
Q&A for science fiction and fantasy enthusiasts
Area 51
Stack Exchange Network staging zone, where users come together to build new Q&A sites
Mathematics
Q&A for people studying math at any level and professionals in related fields
English Language & Usage
Q&A for linguists, etymologists, and serious English language enthusiasts
Electrical Engineering
Q&A for electronics and electrical engineering professionals, students, and enthusiasts
Role-playing Games
Q&A for gamemasters and players of tabletop, paper-and-pencil role-playing games
User Experience
Q&A for user experience researchers and experts
Programmers
Q&A for professional programmers interested in conceptual questions about software development
Server Fault
Q&A for professional system and network administrators
Physics
Q&A for active researchers, academics and students of physics
Meta Stack Overflow
Q&A for meta-discussion of the Stack Exchange family of Q&A websites
Audio-Video Production
Q&A for engineers, producers, editors, and enthusiasts spanning the fields of audio, video, and media creation
Parenting
Q&A for parents, grandparents, nannies and others with a parenting role
Board & Card Games
Q&A for people who like playing board games, designing board games or modifying the rules of existing board games