I have to clarify that the Snap! implementation is 99% the work of Jens Mönig. It was 100% Jens for the first two major releases, back when it was called BYOB ("build your own blocks") and was an extension of the Scratch source code. Then we wanted to use it in a CS course for non-majors at Berkeley so I got in touch with Jens and started complaining about missing features! The result was an intense collaboration in which the coding was still 100% Jens but I contributed ideas about user interface and features. I think my biggest contribution was teaching Jens about lambda!
Our team has officially grown to six people, adding Bernat Romagosa, Jadga Hügle, Michael Ball, and Joan i Pelegay. And several Snap! users have made major contributions, especially to libraries that extend the reach of the language. But the interpreter itself is still all Jens.