Mathematics
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Computational Science
Q&A for scientists using computers to solve scientific problems
Cross Validated
Q&A for statisticians, data analysts, data miners and data visualization experts
Meta Stack Overflow
Q&A for meta-discussion of the Stack Exchange family of Q&A websites
Signal Processing
Q&A for practitioners of the art and science of signal, image and video processing
Programmers
Q&A for professional programmers interested in conceptual questions about software development
Geographic Information Systems
Q&A for cartographers, geographers and GIS professionals
TeX - LaTeX
Q&A for users of TeX, LaTeX, ConTeXt, and related typesetting systems
Electrical Engineering
Q&A for electronics and electrical engineering professionals, students, and enthusiasts
User Experience
Q&A for user experience researchers and experts
Physics
Q&A for active researchers, academics and students of physics
Unix & Linux
Q&A for users of Linux, FreeBSD and other Un*x-like operating systems.