Spoj is an online judge system with over 315000 registered users and over 20000 problems. Developed by Sphere Research Labs
License: Free
Spoj is a competitive programming platform offering a diverse range of coding challenges across multiple languages, while Project Euler is primarily focused on mathematical problems that require algorithmic thinking. Both platforms cater to different audiences, with Spoj appealing to those interested in competitive programming and Project Euler attracting users looking to enhance their mathematical skills through coding.