Mathematics
Q&A for people studying math at any level and professionals in related fields
Database Administrators
Q&A for database professionals who wish to improve their database skills and learn from others in the community
Meta Stack Overflow
Q&A for meta-discussion of the Stack Exchange family of Q&A websites
Cryptography
Q&A for software developers, mathematicians and others interested in cryptography
Unix & Linux
Q&A for users of Linux, FreeBSD and other Un*x-like operating systems.
Programming Puzzles & Code Golf
Q&A for programming puzzle enthusiasts and code golfers
Physics
Q&A for active researchers, academics and students of physics
Game Development
Q&A for professional and independent game developers
Science Fiction & Fantasy
Q&A for science fiction and fantasy enthusiasts
Cross Validated
Q&A for statisticians, data analysts, data miners and data visualization experts
Ask Different
Q&A for power users of Apple hardware and software
Stack Apps
Q&A for apps, scripts, and development with the Stack Exchange API
WordPress Answers
Q&A for WordPress developers and administrators
Theoretical Computer Science
Q&A for theoretical computer scientists and researchers in related fields
Android Enthusiasts
Q&A for enthusiasts and power users of the Android operating system
Programmers
Q&A for professional programmers interested in conceptual questions about software development
Server Fault
Q&A for professional system and network administrators
English Language & Usage
Q&A for linguists, etymologists, and serious English language enthusiasts
Quantitative Finance
Q&A for finance professionals and academics
Answers OnStartups
Q&A for entrepreneurs looking to start or run a new business
Personal Finance & Money
Q&A for people who want to be financially literate
Personal Productivity
Q&A for people wanting to improve their personal productivity
Cognitive Sciences
Q&A for practitioners, researchers, and students in cognitive science, psychology, neuroscience, and psychiatry
Area 51
Stack Exchange Network staging zone, where users come together to build new Q&A sites
Stack Overflow
Q&A for professional and enthusiast programmers