Postgres might not be new, but its popularity has increased in the last year, fuelled by some fantastic releases, like Postgres 10, and its newest features.
Postgres is a great document store, for full text search, for geospatial. And as highlighted here can be used for storing trees or hierarchical data as well.
MVCC and vacuum are core to how Postgres works. Do you understand them? Can you explain them to others? If you answered no to either this post should help.