Stack Overflow
Q&A for professional and enthusiast programmers
Server Fault
Q&A for professional system and network administrators
Cross Validated
Q&A for statisticians, data analysts, data miners and data visualization experts
Role-playing Games
Q&A for gamemasters and players of tabletop, paper-and-pencil role-playing games
Theoretical Computer Science
Q&A for theoretical computer scientists and researchers in related fields
Programmers
Q&A for professional programmers interested in conceptual questions about software development
Mathematics
Q&A for people studying math at any level and professionals in related fields
Cryptography
Q&A for software developers, mathematicians and others interested in cryptography
Programming Puzzles & Code Golf
Q&A for programming puzzle enthusiasts and code golfers
Board & Card Games
Q&A for people who like playing board games, designing board games or modifying the rules of existing board games