Stack Overflow
Q&A for professional and enthusiast programmers
Reverse Engineering
Q&A for researchers and developers who explore the principles of a system through analysis of its structure, function, and operation
Programmers
Q&A for professional programmers interested in conceptual questions about software development
Area 51
Stack Exchange Network staging zone, where users come together to build new Q&A sites
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
Unix & Linux
Q&A for users of Linux, FreeBSD and other Un*x-like operating systems.
Server Fault
Q&A for professional system and network administrators
Cryptography
Q&A for software developers, mathematicians and others interested in cryptography
Mathematics
Q&A for people studying math at any level and professionals in related fields
Android Enthusiasts
Q&A for enthusiasts and power users of the Android operating system
Game Development
Q&A for professional and independent game developers
Meta Stack Overflow
Q&A for meta-discussion of the Stack Exchange family of Q&A websites
Answers OnStartups
Q&A for entrepreneurs looking to start or run a new business