Yes, libhydrogen is a pun, as it is lighter than libsodium.
The first version was a rewrite of libsodium, that was small and contained in a single C file. Also introduced xchacha20 for the first time. Then, the Gimli paper was published, and libhydrogen was rewritten to take advantage of it.
Smaller than libhydrogen, there's now charm: https://github.com/jedisct1/charm , also a pun. The plan was to eventually add bottom (platform abstraction layer), strange (asymmetric cryptography), and top (high-level APIs) to build a modular, component-based library.
> That's a bit light on details. Does it have hardware acceleration? Replay attack protection? Perfect forward secrecy? What are the underlying algorithms? Implementation verified by whom?
More details here: https://github.com/jedisct1/charm
See: https://github.com/jedisct1/charm. That is what it uses.