Meta Stack Overflow
Q&A for meta-discussion of the Stack Exchange family of Q&A websites
English Language & Usage
Q&A for linguists, etymologists, and serious English language enthusiasts
Science Fiction & Fantasy
Q&A for science fiction and fantasy enthusiasts
Mathematics
Q&A for people studying math at any level and professionals in related fields
Cross Validated
Q&A for statisticians, data analysts, data miners and data visualization experts
Area 51
Stack Exchange Network staging zone, where users come together to build new Q&A sites
Physics
Q&A for active researchers, academics and students of physics
Bicycles
Q&A for people who build and repair bicycles, people who train cycling, or commute on bicycles
Audio-Video Production
Q&A for engineers, producers, editors, and enthusiasts spanning the fields of audio, video, and media creation
Unix & Linux
Q&A for users of Linux, FreeBSD and other Un*x-like operating systems.
Musical Practice & Performance
Q&A for musicians, students, and enthusiasts
User Experience
Q&A for user experience researchers and experts
Game Development
Q&A for professional and independent game developers
Stack Apps
Q&A for apps, scripts, and development with the Stack Exchange API
Database Administrators
Q&A for database professionals who wish to improve their database skills and learn from others in the community
Server Fault
Q&A for professional system and network administrators
Programmers
Q&A for professional programmers interested in conceptual questions about software development
TeX - LaTeX
Q&A for users of TeX, LaTeX, ConTeXt, and related typesetting systems
Computer Science
Q&A for students, researchers and practitioners of computer science
Ask Patents
Q&A for people interested in improving and participating in the patent system
Writers
Q&A for authors, editors, reviewers, professional writers, and aspiring writers
Board & Card Games
Q&A for people who like playing board games, designing board games or modifying the rules of existing board games
Answers OnStartups
Q&A for entrepreneurs looking to start or run a new business
Ask Different
Q&A for power users of Apple hardware and software