Mathematics
Q&A for people studying math at any level and professionals in related fields
Stack Overflow
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Super User
Q&A for computer enthusiasts and power users
Unix & Linux
Q&A for users of Linux, FreeBSD and other Un*x-like operating systems
Meta Stack Exchange
Q&A for meta-discussion of the Stack Exchange family of Q&A websites
Puzzling
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Writing
Q&A for the craft of professional writing, including fiction, non-fiction, technical, scholarly, and commercial writing
Server Fault
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Information Security
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Android Enthusiasts
Q&A for enthusiasts and power users of the Android operating system
Academia
Q&A for academics and those enrolled in higher education
Web Applications
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Chemistry
Q&A for scientists, academics, teachers, and students in the field of chemistry
Anime & Manga
Q&A for anime and manga fans
TeX - LaTeX
Q&A for users of TeX, LaTeX, ConTeXt, and related typesetting systems
Biology
Q&A for biology researchers, academics, and students
Cross Validated
Q&A for people interested in statistics, machine learning, data analysis, data mining, and data visualization