The ecosystem is actually bigger, and includes projects such as TweetNaCl.js (pure Javascript implementation), Salt (pure PHP implementation) and Chaos.NaCl (pure C# implementation).
All these projects play well with each other: they have a decent set of primitives and constructions in common, accessible via a very similar API.
http://tweetnacl.cr.yp.to/papers.html
Little is said, other than that TweetNaCl is smaller and thus more easily auditable. No criticism. No pointing out failures. Considering the source, that's IMO a serious compliment. (For comparison, read what is said of OpenSSL...)
So in short, Sodium is a great library. It was forked from NaCl (the most trustable there is) and has some good features added, like scrypt, BLAKE2 and ChaCha.
I think NaCl, TweetNaCl, and Sodium are a great ecosystem, each with different strengths. All great libraries, and the only ones I'd recommend unless you're doing TLS.