VGA Planets has a ship limit of 500 ship in a given game.
At PlanetsCon 2014, the newer, "soft ship limit" called Production Queue was introduced at Planets.nu.
The Classic Queue of VGA Planets has a "hard limit" of 500 ships. Each ship costs 1 PBP ("priority build point") per 50 kt.
The newer Production Queue has a "soft limit" that allows you to build after 500 ships have been reached. After 500 ships, you must spend PP ("priority points") to build. In PQ, building a ship costs 1 extra PP, in addition to the usual 1 PP per 50 kt.