Anything you'd use C or C++ for. Graphics, finance, simulations, native GUI apps, command line tools, etc...

Semantically it's quite C-like, but it's got some nice modern features like a real module system (Odin calls it packages), a project-aware compiler (no build system needed, just run "odin build ." in your project root), fast compile times, and some nice quality of life stuff (good string type, good maths library, built in array maths, some nice built in stuff for memory management). It's also fast. Like in the same ballpark as C, C++ or Rust.

It's basically a modern C replacement.