There's a number of sites that are not open source that use coding tasks like this and tie them with leaderboards and tie-ins to recruiters. As well as hacckerrank, there is codeeval, and there are some others whose names escape me at the moment.

But that doesn't really address a question about putting together an open-source one.

There's also at least one similar-to-Euler one -- rosalind.info (like Euler, but bioinformatics focus) -- which might be closer to responsive, since even though its not open source, their FAQ says they intend to open-source it...

Right, actually I created one as well.