[smurpy]

As a language it is lovely, if you're a fan of minimalism -- being stack-happy, like FORTH. It is well worth learning even just to flex the mind, but especially if you need to make complex diagrams and value stable APIs.

[WillAdams]

METAPOST seems to be similarly stable, and has an interesting programming/math model (DEK keeps it open in window and uses it (or METAFONT which it is based on?) for interactive math).