- A Way to Practice Competitive Programming - Masataka Yoneda (PDF)
- A2 Online Judge
- Algorithms for Competitive Programming
- APL Problem Solving Competition
- AtCoder
- Atcoder DP Contest - Atcoder
- beecrowd
- BigFrontEnd.dev
- COCI
- Codeabbey
- Codechef
- Codecombat
- Codeeval
- CodeFights
- Codeforces
- Codeground
- Coderbyte
- Codewars
- Codingame
- Competitive Programming Cheat Sheet
- CSES Problem Set
- Dimik
- DMOJ
- E-olymp
- Exercism
- Frontend Coding Challenges - FrontendAtlas
- HackerEarth
- Hackerrank
- Internet Problem Solving Contest
- JSCodebox
- Just another Golf Coding
- Kattis
- Last Moment DSA Sheet(79) – Ace Interviews - Striver
- LeetCode
- LightOJ
- Meta Hackercup
- Newton School
- oj.uz
- Sigmageek
- Sphere Online Judge
- Techgig
- Top Array Interview Questions – Structured Path with Video Solutions | Arrays Series
- Top Coding Interview Problems - Striver
- Topcoder
- Toph
- USACO.guide
- ångstromCTF
- CTFlearn (email address requested)
- CTFtime
- DamnVulnerableDefi
- echoCTF (email address requested)
- Google CTF (email address requested)
- Hacker101 (email address requested)
- Hackthebox (email address requested)
- HackThisSite (email address requested)
- InCTF
- Microcorruption
- Overthewire Wargames fungame to practice CTF
- Picoctf (email address requested)
- ringzer0ctf (email address required)
- ROP Wargame Repository
- SmashTheStack
- TryHackMe (email address requested)
- Frontend Mentor (email address requested)
- A2 Online Judge
- Atcoder Problems
- C2 Ladders
- Striver's A2Z DSA Course/sheet
- Striver’s CP Sheet
- System Design Roadmap with Videos for SDEs - take U forward(takeuforward)
- #C++ - Keerti Purswani
- 100 Days CSS Challenge - Matthias Martin (Codepen account requested, not required)
- 500 Data structures and algorithms interview questions and their solutions in C++
- Abekus | Free Practice Questions with Solutions
- 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
- Grind 75
- Hacker.org
- HackerEarth
- HDU Online Judge
- IndiaBix
- Interactive Coding Challenge
- InterviewBit
- Kattis
- Mathproblem of the Month - Bilkent University
- NeetCode 150
- PEG Judge
- Pep Coding
- PKU Online Judge
- Ponder This!
- PracHub
- 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
- Top Interview 150 - LeetCode
- Topic wise multiple choice questions in computer science - Geeks For Geeks
- UVa Online Judge
- Vulnhub.com
- Школа программиста