Ruby on Rails
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Users can submit new programming challenges, and do them. You have PBL's (points, badges, leaderboards) to track progression. Challenges can be simple (add two integers together) and complex (train a neural network). The idea is to get people involved with very easy challenges and keep them motivated with a ladder. The scripts for validating challenges are run on the server (?) or called via an API. They are validated manually by a webmaster.