hackattic - No nonsense, real world programming challenges
NumWorks - The graphing calculator that makes learning math easier.
Code Fight Club - A fight club you can talk about. Less punching, more coding.
Learney - Knowledge aggregator for developers
Codewars - Achieve code mastery through challenge.
eMathHelp.net - Site is created to help people learn math. Includes algebra, calculus, differential equation calculators and notes with many examples.