Bicycles
Q&A for people who build and repair bicycles, people who train cycling, or commute on bicycles
Server Fault
Q&A for professional system and network administrators
Database Administrators
Q&A for database professionals who wish to improve their database skills and learn from others in the community
Programmers
Q&A for professional programmers interested in conceptual questions about software development
Geographic Information Systems
Q&A for cartographers, geographers and GIS professionals
Electrical Engineering
Q&A for electronics and electrical engineering professionals, students, and enthusiasts
Android Enthusiasts
Q&A for enthusiasts and power users of the Android operating system
English Language & Usage
Q&A for linguists, etymologists, and serious English language enthusiasts
Physics
Q&A for active researchers, academics and students of physics
WordPress Answers
Q&A for WordPress developers and administrators
Meta Stack Overflow
Q&A for meta-discussion of the Stack Exchange family of Q&A websites
Unix & Linux
Q&A for users of Linux, FreeBSD and other Un*x-like operating systems.
Software Quality Assurance & Testing
Q&A for software quality control experts, automation engineers, and software testers