- 4Clojure
- A2 Online Judge
- Codeabbey
- Codechef
- Codecombat
- Codeeval
- CodeFights
- Codeforces
- Coderbyte
- Codewars
- Codingame
- Facebook Hackercup
- HackerEarth
- Hackerrank
- Hello World Open
- Internet Problem Solving Contest
- Just another Golf Coding
- Kattis
- Microcorruption
- Saratov State University
- Sphere Online Judge
- Topcoder
- A2 Online Judge
- Advent Of Code
- Anarchy Golf
- CareerCup
- CheckIO
- Codeforces
- CodeHunt
- Codility
- Coding Bat
- Exercism
- Geeks For Geeks
- Google Code Jam - Practise
- Hacker.org
- HackerEarth
- HDU Online Judge
- InterviewBit
- Kattis
- Leetcode
- Mathproblem of the Month - Bilkent University
- PEG Judge
- PKU Online Judge
- Ponder This!
- ProblemBook.NET
- Project Euler
- Python Practice Projects
- Rosalind
- Sphere Online Judge
- TalentBuddy
- Timus Online Judge
- URI Online Judge
- UVa Online Judge