Pretty much the same as the Character Dumping... (see note in the Public Domain Characters section) when it comes to the "legal" stuff but this time it's with Worlds!
Again, the more information you give about the worlds you have created, the more usable it will be for other people! Of course it doesn't have to be the most well-rounded and fully constructed place ever. Worlds can mean any type of setting from expansive galactic empires to an office building. Heck, even, say, giving over a cool idea of a passageway that leads from a trashcan to an underground ice cream shop would be cool. Taking bits from one world and putting them into others is what i envision happening often. Worlds can also include gadgets and vehicles and accessories. basically anything that doesn't have socially-agreed sentience and isn't a story. The Things.
Also again, post a reply if you use anything you see here, if not to give thanks to the person who brought it to The PUBLIC DOMAIN! and please, only your own creations or what is already noncopyrighted. though we don't adhere much to copyrights, we don't want to infringe on those who do.
besides that, have fun, go nuts!
Rv. Xen