Former Maths student at Cambridge (my fourth-year courses were in logic/computability/set theory and also combinatorics); now a software engineer.
Mathematics
Q&A for people studying math at any level and professionals in related fields
English Language Learners
Q&A for speakers of other languages learning English
Academia
Q&A for academics and those enrolled in higher education
Worldbuilding
Q&A for writers/artists using science, geography and culture to construct imaginary worlds and settings
Stack Overflow
Q&A for professional and enthusiast programmers
Puzzling
Q&A for those who create, solve, and study puzzles
English Language & Usage
Q&A for linguists, etymologists, and serious English language enthusiasts
Mathematics Educators
Q&A for those involved in the field of teaching mathematics
Science Fiction & Fantasy
Q&A for science fiction and fantasy enthusiasts
Economics
Q&A for those who study, teach, research and apply economics and econometrics
Programming Language Design and Implementation
Q&A for designers and implementers of computer programming languages
Interpersonal Skills
Q&A for people looking to improve their interpersonal communication skills
Board & Card Games
Q&A for people who like playing board games, designing board games or modifying the rules of existing board games
Quantum Computing
Q&A for engineers, scientists, programmers, and computing professionals interested in quantum computing
Latin Language
Q&A for linguists, teachers, and students wanting to discuss the finer points of the Latin language
Writing
Q&A for the craft of professional writing, including fiction, non-fiction, technical, scholarly, and commercial writing
TeX - LaTeX
Q&A for users of TeX, LaTeX, ConTeXt, and related typesetting systems
Linguistics
Q&A for professional linguists and others with an interest in linguistic research and theory
Philosophy
Q&A for those interested in the study of the fundamental nature of knowledge, reality, and existence
Code Review
Q&A for peer programmer code reviews
Biblical Hermeneutics
Q&A for professors, theologians, and those interested in exegetical analysis of biblical texts
Christianity
Q&A for committed Christians, experts in Christianity and those interested in learning more
Personal Finance & Money
Q&A for people who want to be financially literate
Computer Science
Q&A for students, researchers and practitioners of computer science
Japanese Language
Q&A for students, teachers, and linguists wanting to discuss the finer points of the Japanese language
Literature
Q&A for scholars and enthusiasts of literature
Computer Science Educators
Q&A for those involved in the field of teaching Computer Science
Artificial Intelligence
Q&A for people interested in conceptual questions about life and challenges in a world where "cognitive" functions can be mimicked in purely digital environment
Space Exploration
Q&A for spacecraft operators, scientists, engineers, and enthusiasts
Open Source
Q&A for people organizing, marketing or licensing open source development projects
History of Science and Mathematics
Q&A for people interested in the history and origins of science and mathematics
The Workplace
Q&A for members of the workforce navigating the professional setting
Music: Practice & Theory
Q&A for musicians, students, and enthusiasts
Cross Validated
Q&A for people interested in statistics, machine learning, data analysis, data mining, and data visualization
Code Golf
Q&A for programming puzzle enthusiasts and code golfers
MathOverflow
Q&A for professional mathematicians
Politics
Q&A for people interested in governments, policies, and political processes
Astronomy
Q&A for astronomers and astrophysicists
Ask Different
Q&A for power users of Apple hardware and software
Database Administrators
Q&A for database professionals who wish to improve their database skills and learn from others in the community
Chess
Q&A for serious players and enthusiasts of chess
Software Engineering
Q&A for professionals, academics, and students working within the systems development life cycle
Data Science
Q&A for Data science professionals, Machine Learning specialists, and those interested in learning more about the field
Unix & Linux
Q&A for users of Linux, FreeBSD and other Un*x-like operating systems
Physical Fitness
Q&A for physical fitness professionals, athletes, trainers, and those providing health-related needs
Quantitative Finance
Q&A for finance professionals and academics
Proof Assistants
Q&A for mathematicians and computer scientists who develop and use proof assistants
Meta Stack Exchange
Q&A for meta-discussion of the Stack Exchange family of Q&A websites
Physics
Q&A for active researchers, academics and students of physics