Ok, I finally got around to download the damn thing and take a look. It's just a toy programming language, with a C-style syntax and an ugly function naming convention. And yes, it's terribly slow.

@MyNameIsNobody: Thanks for your help
@kesadisan: OsoScript allows you to write your own programs and run them on the DS without the need to set up a complete toolchain. Maybe it can be used for very simple games/demos but not much more. At least in its current state.