Area 51
Stack Exchange Network staging zone, where users come together to build new Q&A sites
Server Fault
Q&A for professional system and network administrators
Geographic Information Systems
Q&A for cartographers, geographers and GIS professionals
Programmers
Q&A for professional programmers interested in conceptual questions about software development
Personal Finance & Money
Q&A for people who want to be financially literate
Meta Stack Overflow
Q&A for meta-discussion of the Stack Exchange family of Q&A websites
English Language & Usage
Q&A for linguists, etymologists, and serious English language enthusiasts
Bicycles
Q&A for people who build and repair bicycles, people who train cycling, or commute on bicycles
Theoretical Computer Science
Q&A for theoretical computer scientists and researchers in related fields
WordPress Answers
Q&A for WordPress developers and administrators
Cross Validated
Q&A for statisticians, data analysts, data miners and data visualization experts
Unix & Linux
Q&A for users of Linux, FreeBSD and other Un*x-like operating systems.
Stack Apps
Q&A for apps, scripts, and development with the Stack Exchange API
Mathematics
Q&A for people studying math at any level and professionals in related fields
Answers OnStartups
Q&A for entrepreneurs looking to start or run a new business
Writers
Q&A for authors, editors, reviewers, professional writers, and aspiring writers