Is MongoDB the leader in NoSQL? I stopped using them years ago because of scaling issues. With things like Elastic Search and Dynamo DB, I see no reason to use MongoDB anymore.
Couchbase is an enterprise grade NoSQL database, it scales very well, and it has a full SQL-like query language, and a lot of large companies use it.
The community edition is free as in free beer and it is also open source. For enterprise use, you can buy a support contract, and there is an enterprise edition.
I wanted to also add that it makes a difference if you only want one server or not. A good small Couchbase cluster has at least 3 nodes.
If you have VirtualBox, puppet and vagrant, this makes it ridiculously easy to bring up a small cluster:
https://github.com/couchbaselabs/vagrants
Note: you still have to use the UI to configure the cluster but this gets the nodes (VMs) up and running quickly.
Joking aside, SQLite is on a ton of devices, yes. But that's primarily because it ships with OS's and is in lots of embedded devices. For web development and other server-side things, I get the feeling that SQLite is not as heavily used as client-server databases.