CodeSignal - CodeSignal is the leading assessment platform for technical hiring.

UFO Hunt - Data from the National UFO Reporting Center.

Code Arcade - Complete coding tasks to advance levels in this arcade for programmers.

CodinGame - CodinGame provides users with a fun and effective way to learn coding that eschews the rigid structure of traditional teaching methods.

Out There - Out There is a space exploration game blending resource management and gamebook with no combat.

hackattic - No nonsense, real world programming challenges