Physical Fitness
Q&A for physical fitness professionals, athletes, trainers, and those providing health-related needs
Stack Overflow
Q&A for professional and enthusiast programmers
Unix & Linux
Q&A for users of Linux, FreeBSD and other Un*x-like operating systems.
Game Development
Q&A for professional and independent game developers
Area 51
Stack Exchange Network staging zone, where users come together to build new Q&A sites
Mathematics
Q&A for people studying math at any level and professionals in related fields
Academia
Q&A for academics and those enrolled in higher education
Programmers
Q&A for professional programmers interested in conceptual questions about software development
TeX - LaTeX
Q&A for users of TeX, LaTeX, ConTeXt, and related typesetting systems
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
Linguistics
Q&A for professional linguists and others with an interest in linguistic research and theory
Genealogy & Family History
Q&A for expert genealogists and people interested in genealogy or family history