I don't know why you've been downvoted. The interface does look neat. They did a good job with it.

Other example of such thing is Numberjack -- a constraint solve with multiple backends:

http://numberjack.ucc.ie/

Here is a send-more-money example solved in it:

http://numberjack.ucc.ie/examples/sendmoremoney

Sudoku:

https://github.com/eomahony/Numberjack/blob/master/examples/...