The idea is cool. Slant does something, but not really similar to what you want.

That's what Documentation and Rosetta Code both are. These are not coding challenge sites.

It seems similar but the examples are fairly short. I'd want multiple submissions from the same language for instance build a simple web service with N endpoints and error handling. Then someone submits Spring, J2EE, Play and lower level framework examples all solving the same web service task.