Just a thought

[Pbcrazy]

Bradyok from xtremeworlds made his engine and jerrath mmorpg based of it
and Griever,Jeff Ninja and Nero made X-realms Engine and eteranl mercenariaes mmorpg using there engine

but they had to make the engine to make thier game, plus its not really an engine as much as a game editor, so once they finished the engine/editor they decided to release it to he public and still make thier game. so essentially they did what Robin is doing.