I've been using japaric's awesome work on Xargo (for cross compiling the std lib) to target a variety of ARM Cortex'es. Sometimes doing all work in Rust, sometimes just for linking against Rust crates in a C program. It's a breeze and super fun.

This is, in my opinion, where Rust really shines: using one codebase - without installing any new tools - I can target pretty much all platforms from embedded to browser to mobile.