Area 51
Stack Exchange Network staging zone, where users come together to build new Q&A sites
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.
Meta Stack Overflow
Q&A for meta-discussion of the Stack Exchange family of Q&A websites
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
Physics
Q&A for active researchers, academics and students of physics
Ask Different
Q&A for power users of Apple hardware and software
Game Development
Q&A for professional and independent game developers
Role-playing Games
Q&A for gamemasters and players of tabletop, paper-and-pencil role-playing games
Photography
Q&A for professional, enthusiast and amateur photographers
User Experience
Q&A for user experience researchers and experts
Science Fiction & Fantasy
Q&A for science fiction and fantasy enthusiasts
Server Fault
Q&A for professional system and network administrators
LEGO® Answers
Q&A for LEGO® and building block enthusiasts
Parenting
Q&A for parents, grandparents, nannies and others with a parenting role
The Workplace
Q&A for members of the workforce navigating the professional setting
Musical Practice & Performance
Q&A for musicians, students, and enthusiasts
Academia
Q&A for academics and those enrolled in higher education