This looks more like a Mongoose than like a Firebase/Firestore clone :/ You need a MongoDB instance somewhere, so this is not really a database library, it's more like query (ORM?) thing. Looks interesting nevertheless.

While not free, Firebase and Firestore have a really generous free plan quota, but big downside, in my opinion, is unnecessary complexity around setting up and working with them.

Also, there is no cloud 😛 it's just a server somewhere.