Coding Practice Platforms

These are the sites where people actually become programmers. Project-based curricula and problem-solving repetition consistently beat passive video courses. For the in-page editors that power them see Code Editors & Playgrounds; for full curricula see Code Bootcamps & Curriculum; for kid-shaped versions see K-12 Coding.

The gold standard, free + FOSS

• ★ ★ freeCodeCamp — BSD-3 + creative commons; ~3,000-hour curriculum across web, JS, data analysis, ML, college math; fully free; certifications free; non-profit; mainstream success story (millions of learners). Self-host the platform locally if you want.
  • https://github.com/freeCodeCamp/freeCodeCamp
• ★ The Odin Project — AGPL; project-heavy full-stack curriculum (Ruby track + JS track); free; pairs with a Discord-led community.
  • https://github.com/TheOdinProject/theodinproject
• ★ CS50 (Harvard) — free on edX (audit) + open courseware; David Malan; the canonical intro. Tracks: CS50x (general), CS50P (Python), CS50W (web), CS50AI, CS50SQL.
• ★ Exercism — MIT; mentored coding practice in 70+ languages; mentor feedback is free; the best way to "learn a second language quickly." FOSS exercise content.
  • https://github.com/exercism

Problem-of-the-day / interview prep

• ★ LeetCode — free + paid (Premium); the interview-prep default. ~3,500 problems; "Top Interview 150" curated list.
• ★ NeetCode — free + paid; LeetCode roadmap with curated 150 / 250 / "all" lists, free YouTube walkthroughs; the structure most candidates recommend.
• Codewars — free + paid; community-authored "kata"; many languages; good for fluency drills.
• HackerRank — free + paid; corporate-recruiting backbone; certificates; DSA + SQL + JS / React tracks.
• CodeSignal — free + paid; recruiting-focused; "Arcade" and "GCA" tests.
• AlgoExpert / SystemsExpert — paid; curated 169 questions + system design course; popular upgrade from LeetCode.
• InterviewBit — free + paid; structured DSA tracks with mock interviews.
• Edabit, Coderbyte, HackerEarth — alternatives.

Topic-specific practice

• AdventOfCode — free; one puzzle per day in December; cult following.
• Project Euler — free; mathematical / computational puzzles.
• Cryptopals — free; cryptography puzzles by NCC Group.
• CodinGame — free + paid; bot battles + puzzles in a game UI.
• Codeforces / AtCoder / TopCoder — free competitive programming.
• CodeChef / SPOJ / UVa Online Judge — older competitive judges.
• Pwn College / picoCTF / OverTheWire — security / CTF practice; free.
• Frontend Mentor — paid + free; HTML/CSS/JS challenges with real Figma designs.
• Codewell, DevChallenges.io — alternative front-end challenge sites.
• Build Your Own X — free GitHub repo / curriculum collection of "build a Git from scratch" projects; one of the best free resources online.
  • https://github.com/codecrafters-io/build-your-own-x
• CodeCrafters — paid; "build your own Redis / Git / shell" with a polished test runner.

Hosted with mentors / cohorts

• Boot.dev — paid + free first chapters; Go-flavoured back-end curriculum + community; popular.
• Scrimba — paid + free; "interactive screencast" format; Frontend / React focused.
• Educative — paid; text-first courses with embedded code; quick to skim.
• Codecademy — paid + free; in-page editor; classic intro path.
• Brilliant.org — paid + free trial; CS / math / data; gamified; great for visual thinkers.
• Datacamp — paid + free; data / Python / R focused.

Pick this if…

• Default free, project-based, full-stack: freeCodeCamp + The Odin Project.
• Canonical intro to CS: CS50.
• Learn a new language fast, with mentors: Exercism.
• Coding-interview prep: NeetCode roadmap → LeetCode → AlgoExpert if budget allows.
• Competitive programming: Codeforces or AtCoder.
• Front-end real-design challenges: Frontend Mentor.
• Back-end Go-flavoured paid: Boot.dev.
• Build-from-scratch project mode: Build Your Own X (free) or CodeCrafters (paid).