Have been playing it for a while, so I thought I'd share... Codingame
Its a game that requires you to write programs and output data based on input. You can use the language you prefer and the difficulty curve is great. It has Pathfinding, Greedy algorithms, Triangulation and all sorts of puzzles from Easy to Very Hard.
There is also an Online Battle style mode, where you compete with other programmers (or write bots that compete with other bots).
By the way, I think its open-source and community developed, or at least I saw a GitHub somewhere...
PS.: If anyone is playing, say, there is an option to invite a friend to a match