- Sites/
- Project Euler
- Kaggle
- HackerRank
- Ckeckio
- JavaScript30
- TopCoder
- CodeWars
- CodeForces
- AdventOfCode - 25 days of themed coding challenges, starting each year on Dec 1.
- LeetCode
- Project Lovelace - free scientific programming problems.
- Exercism.io
- PythonChallenge
- CodeSignal
- HackerEarth
- edabit
- Rosalind - Python ∩ Biology
- practiceJS - some JavaScript coding exercises put into a web app so they can be done on a phone.
- CodinGame