WHAT PostgreSQL IS DOING TO WINDOW FUNCTIONS, WILL SHAKE YOU TO YOUR CORE!
On a serious note, PostgreSQL is the epitome, IMHO, of an open-source project that is tightly managed, but still able to change with the times and the user-bases changing needs. Really Postgres and Redis are the two projects that I think of when I think about "great" open-source projects.
What they mean is that for years, Postgres had the most advanced support for window functions among the common databases. Then they lost that crown due to an update to MySQL, but now with 11, they are back to being the leader as they have brought in the missing feature plus some additional ones.
On a serious note, PostgreSQL is the epitome, IMHO, of an open-source project that is tightly managed, but still able to change with the times and the user-bases changing needs. Really Postgres and Redis are the two projects that I think of when I think about "great" open-source projects.