Bicycles
Q&A for people who build and repair bicycles, people who train cycling, or commute on bicycles
Homebrewing
Q&A for dedicated home brewers and serious enthusiasts
Programmers
Q&A for professional programmers interested in conceptual questions about software development
Musical Practice & Performance
Q&A for musicians, students, and enthusiasts
The Great Outdoors
Q&A for people who love outdoor activities, excursions, and outdoorsmanship
Server Fault
Q&A for professional system and network administrators
Physical Fitness
Q&A for physical fitness professionals, athletes, trainers, and those providing health-related needs
Meta Stack Overflow
Q&A for meta-discussion of the Stack Exchange family of Q&A websites
Sports
Q&A for participants in team and individual sport activities
Cross Validated
Q&A for statisticians, data analysts, data miners and data visualization experts
Mathematics
Q&A for people studying math at any level and professionals in related fields
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.
Electrical Engineering
Q&A for electronics and electrical engineering professionals, students, and enthusiasts
Database Administrators
Q&A for database professionals who wish to improve their database skills and learn from others in the community
Android Enthusiasts
Q&A for enthusiasts and power users of the Android operating system
Personal Finance & Money
Q&A for people who want to be financially literate
Motor Vehicle Maintenance & Repair
Q&A for mechanics and DIY enthusiast owners of cars, trucks, and motorcycles
Area 51
Stack Exchange Network staging zone, where users come together to build new Q&A sites