Is there a crate that provides a map-like data structure where keys only need to implement `Eq`?

All map implementations I've seen require that keys are either Hash or Ord, because they construct either a hash table or a binary tree, for log-complexity lookup.

However, sometimes you need to work with keys that only implement Eq. A map-like data structure is still possible for such keys, via a simple linear search over all keys contained in the map.

Is there a crate that provides such a data structure, with an API similar to the std::collections maps?

Bonus question: Why doesn't the standard library define a Map trait? It looks like 90% of HashMap's and BTreeMap's methods are the same, but that common interface is not encapsulated in a shared trait. Why not?