Back when Dart first came out (I think 0.1), I built a gravity simulator in it. It was a shameless rip-off of http://www.nowykurier.com/toys/gravity/gravity.html, but it was just for me to get a little familiar with it.

It was pretty dang great writing that project, and I'm beyond surprised that Dart didn't have more success in replacing JS.

I unfortunately lost the source code at some point :( (this was before I got organized, got a GitHub, etc).