Edit: Replying to ghusbands:
'unsafe' is a core part of Rust itself, not a separate language. And it occurs often in some types of Rust projects or their dependencies. For instance, to avoid bounds checking and not rely on compiler optimizations, some Rust projects use vec::get_unchecked, which is unsafe. One occurrence in code is here:
https://grep.app/pola-rs/polars/main/crates/polars-io/src/cs...
And there are other reasons than performance to use unsafe, like FFI.
Edit2: ghusbands had a different reply when I wrote the above reply, but edited it since.
Edit3: Ycombinator prevents posting relatively many new comments in a short time span. And ghusbands is also wrong about his answer not being edited without him making that clear.