[Sharlin]

The `core` library is still available on `no_std` and contains a lot of useful stuff, so it’s not exactly like no libc on C. That would be `no_core` which is pretty hardcore (heh). The big things missing in `no_std` are

* file and other I/O, including filesystem ops

* access to system time

* threads

* collections and some other things that require an allocator (not many things actually do in Rust’s stdlib!)

* floating-point functions (the types themselves and builtin operators work fine)

`alloc` gives you `Vec`, `String`, `Box`, `BTreeMap/Set`, ref-counted pointers, and a few `Vec`-derived collections like `VecDeque`. Very annoyingly not `HashSet/Map` though, due to a literally single-line dependence on a system entropy source which happens to not be easily factorable out because reasons.