stockfighter https://starfighter.readme.io/
It's a video game, except to play you are writing software - or - a bot - to compete in a virtual stock market. To play, you consume REST / Websocket endpoints analyzing the orderbook / market data and trading against it. There are levels with different objectives.
https://news.ycombinator.com/item?id=10724592
http://www.kalzumeus.com/2015/08/20/designing-and-building-stockfighter-our-programming-game/
###I'm using my own api/wrapper/client from here: https://github.com/kdawes/node-stockfighter