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
Physics
Q&A for active researchers, academics and students of physics
Programmers
Q&A for professional programmers interested in conceptual questions about software development
Unix & Linux
Q&A for users of Linux, FreeBSD and other Un*x-like operating systems.
User Experience
Q&A for user experience researchers and experts
Ask Different
Q&A for power users of Apple hardware and software
Cross Validated
Q&A for statisticians, data analysts, data miners and data visualization experts
English Language & Usage
Q&A for linguists, etymologists, and serious English language enthusiasts
Server Fault
Q&A for professional system and network administrators
Meta Stack Overflow
Q&A for meta-discussion of the Stack Exchange family of Q&A websites
Game Development
Q&A for professional and independent game developers
Stack Apps
Q&A for apps, scripts, and development with the Stack Exchange API
TeX - LaTeX
Q&A for users of TeX, LaTeX, ConTeXt, and related typesetting systems
Answers OnStartups
Q&A for entrepreneurs looking to start or run a new business
Signal Processing
Q&A for practitioners of the art and science of signal, image and video processing
Physical Fitness
Q&A for physical fitness professionals, athletes, trainers, and those providing health-related needs
Programming Puzzles & Code Golf
Q&A for programming puzzle enthusiasts and code golfers