Project Euler is a series of challenging mathematical/computer programming problems that will require more than just mathematical insights to solve.
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.