Ask HN: Ideas for Rust projects?

Check out the tasks on Rosetta Code (rosettacode.org). That's a good way to get started with any new language, and you may find that one of the tasks inspires you to do something more complex.

Not exactly low level programming, but you can try the Matasano crypto challenge: http://cryptopals.com/

A binding to the CUPS server, lack of printing capabilities surprised me

game development frameworks and libraries!