- 4Clojure
- A2 Online Judge
- Algorithms for Competitive Programming
- APL Problem Solving Competition
- AtCoder
- beecrowd
- Binary Search
- COCI
- Codeabbey
- Codechef
- Codecombat
- Codeeval
- CodeFights
- Codeforces
- Codeground
- Coderbyte
- Codewars
- Codingame
- Competitive Programming Cheat Sheet
- CSES Problem Set
- Dimik
- DMOJ
- E-olymp
- Exercism
- HackerEarth
- Hackerrank
- Internet Problem Solving Contest
- Just another Golf Coding
- Kattis
- LeetCode
- LightOJ
- Meta Hackercup
- Microcorruption
- Newton School
- oj.uz
- Sigmageek
- Sphere Online Judge
- Striver’s CP Sheet
- Techgig
- Topcoder
- Toph
- USACO.guide
- CTFlearn (email address requested)
- Google CTF (email address requested)
- Hacker101 (email address requested)
- Hackthebox (email address requested)
- HackThisSite (email address requested)
- Overthewire Wargames fungame to practice CTF
- Picoctf (email address requested)
- SmashTheStack
- TryHackMe (email address requested)
- 500 Data structures and algorithms interview questions and their solutions in C++
- A2 Online Judge
- Advent Of Code
- AdventJS - 25 días de retos con JavaScript - Miguel Ángel Durán «midudev» (GitHub account requested, not required)
- Anarchy Golf
- APL Practice Problems
- BaekJoon Online Judge
- beecrowd
- CareerCup
- CheckIO
- Codechef
- Codedrills
- Codeforces
- Codility
- Coding Bat
- Coding Interview Questions and answers for practice | Python, Java & C++ - CodingNinjas
- Coding Ninjas Guided Paths
- CSES Problem Set
- DSA Learning Series
- Dynamic A2OJ Ladder
- Edabit
- Exercism
- Geeks For Geeks
- Hacker.org
- HackerEarth
- HDU Online Judge
- Interactive Coding Challenge
- InterviewBit
- Kattis
- Leetcode
- Mathproblem of the Month - Bilkent University
- PEG Judge
- Pep Coding
- PKU Online Judge
- Ponder This!
- Practice Python
- ProblemBook.NET
- Project Euler
- Python Practice Projects
- Rosalind
- Sphere Online Judge
- TalentBuddy
- The Ultimate Topic List(with Tutorials, Problems, and Templates) - Shahjalal Shohag
- Timus Online Judge
- Topic wise multiple choice questions in computer science - Geeks For Geeks
- UVa Online Judge
- Vulnhub.com
- Школа программиста