UnQLite is the NoSQL variant of SQLite. I suppose if I needed a document store I’d probably go after one of the big boys like RethinkDB, MongoDB, or even Oracle. There are even a plugin or two for Postgres.
And if I needed a key/value store there is Riak, Redis, a number of embedded libraries and of course there also SQLite since k/v stores are just the 5th normal form (or something like that).
But if I needed a small pragmatic storage engine for storing documents or some UnSQLite -like data… I’m not sure I’d ever go embedded with UnQLite. I suppose that’s why the SQLite author never completed his UnQLite project.