Codewars!

A fun social platform for hackers to solve interesting puzzles, build quick hacks, code game bots and collaborate to solve real-world challenges.

Project Euler is a series of challenging mathematical/computer programming problems that will require more than just mathematical insights to solve. Although mathematics will help you arrive at elegant and efficient methods, the use of a computer and programming skills will be required to solve most problems.

Duel with friends and foes in head-to-head programming battles!

Coderbyte is a place built for anyone to practice and perfect their programming skills. Challenges are added almost every day so you can work on applying your algorithmic thought process on any problem you want at anytime. Coderbyte is built on improving your ability to work on common logic, mathematical, and algorithmic problems you might one day encounter.

CheckiO is expanding the world’s code literacy through gameplay.

SPOJ (Sphere Online Judge) is an online judge system with over 315,000 registered users and over 20000 problems. The solution to problems can be submitted in over 60 languages including C, C++, Java, Python, C#, Go, Haskell, Ocaml, and F#. SPOJ has a rapidly growing problem set/tasks available for practice 24 hours/day, including many original tasks prepared by the community of expert problem setters associated with the project.

Learn to code (for free) with interactive challenges. Gain XP, unlock achievements and climb the leaderboard. It's the fastest, easiest, most addictive way to learn.

Devskiller is an online testing platform that helps companies verify programming skills. It’s designed to directly address the key problems of hiring the IT talent: • Programming skills quality assessmentDevskiller helps to verify tech skills of programming languages, frameworks and libraries, imitating a real programming environment.• Customized online testingAssessing candidates at the first screening step results in a smaller, better-qualified and suited IT candidate pipeline before the time-consuming process of interviewing.• HR user-friendly toolDevskiller is easy to use for staff with no technical background, decreasing high costs of engaging the tech team.• EducationDevskiller helps also to evaluate the progress of education of programmers.In short, our customers use the platform to reduce the number of unnecessary interviews by 60-70% and to decrease the time-to-hire by 30-50%. »

CodeEval is platform for hosting coding challenges which has over 20,000+ competitive developers.

This version of Ruby Warrior is a project by Bloc, a part-time online coding bootcamp for people who want to keep their current job, learn how to code, and become a full-time software developer.

CodeChef was created by Directi as a way to continuously challenge and engage the developer community. Our goals are to provide a platform for practice, competition and improvement as well as enable developers to benchmark their skills against their peers. We’re having fun with the site and hope you will too.

VIM Adventures is an online game based on VIM's keyboard shortcuts (commands, motions and operators). It's the "Zelda meets text editing" game. It's a puzzle game for practicing and memorizing VIM commands (good old VI is also covered, of course). It's an easy way to learn VIM without a steep learning curve.You play a blinking cursor appearing one day in a semi text based world of Textland inhabited by little people but ruled by bugs. You soon discover that your arrival was foretold by an old prophecy and that you're expected to restore order to the world (in case you didn't make it to level 2 yet...). »

Topcoder gathers the world’s experts in design, development and data science to work on interesting and challenging problems. Members are provided with opportunities to demonstrate their expertise, improve their skills, and win cash, while helping real world organizations solve real world problems.

At Geektastic we help our client's thoroughly evaluate their future talent using our unique peer reviewed code challenge platform. We believe a candidate is worth more than a score and the only way to thoroughly understand how suitable they are to work in your team is to have a human look over their code. The platform allows clients to license code challenges from our portfolio or upload their own, they can also choose to have our on-demand team (of exceptionally talent software engineers) carry out the thorough review or perform it in-house. »

Kattis helps companies make safer recruitments and attract the best developers with its dynamic challenge platform.