https://github.com/rust-lang/hashbrown is a port of Google's SwissTable algorithm (abseil flat_hash_map). It also uses SIMD filtering and has the potential to be quite good.
Which has been recently upstreamed to the standard library, replacing the old hash map implementation. (This sped up rustc a noticeable amount, incidentally.)
Is `hashbrown::HashMap` now completely ported/identical with `std::collections::HashMap`? I just compared their performance (on yesterday's beta channel) on a hashmap with over 200k keys and didn't notice any relevant speedup.