I'd like to self-nominate one package we use heavily for high-performance unique identifier generation;
It is half the size (64 bytes) and usually significantly higher performance for generation than using UUID:s.
It is likely overkill for most casual users who would be fine with UUID:s, but for certain use cases where memory costs and generation performance matters it can be very useful.
There are some caveats noted in the documentation (specifically, for distributed systems a generator identifier must be assigned to each producer to guarantee uniqueness).