My hobbies include doing research mathematics, doing elementary mathematics, writing things in latex, cooking, correcting grammar, and being skeptical. Fortunately there is a stackexchange website for each of these compulsions.
Q&A for people studying math at any level and professionals in related fields
Q&A for professional mathematicians
Q&A for users of TeX, LaTeX, ConTeXt, and related typesetting systems
Q&A for scientific skepticism
Q&A for professional and amateur chefs
Q&A for linguists, etymologists, and serious English language enthusiasts
Q&A for professional and enthusiast programmers