Does this handle connection pooling? I notice that in the README, the example establishes a connection to the database, and then the Express app runs. Is this a single connection for the entire time the node app is running in a process (yikes!), or is there some sort of connection pooling going on in the background with this?

Yes there's connection pooling. But it's handled by the underlying PG library https://github.com/brianc/node-postgres that Massive is based on.

A .NET library with the name "Massive" already exists with similar functionality: https://github.com/FransBouma/Massive

Is there any inspiration/connection between the two?

They're both created by the same author, Rob Conery. Frans has taken over maintenance of Massive 1.0.

Can be tweaked to quickly used as the REST API on top of Postgres