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A good plugin, just needs more popularity.
This is a very good plugin. It does need a few more developers, and, since it's free, a few more people trying to download it. The editor is free for Unity 2.6, but is difficult to use. There are several gems for it out there, including Mars Explorer, WolfQuest, and a few other games.
Pros: Incredible graphics, easy to download, doesn't take up much space
Cons: High CPU demand, can use up bandwidth depending on the game, not a lot of support