File Share

The File Share is a feature in Halo 3 which allows players to upload custom content for others to view and download. This content include game films, film clips, map variants, gametypes and screenshots. By default, players may upload up to six custom content items, but may subscribe to "Bungie Pro," which allows them up to twenty-four upload slots for 750 Microsoft points. For a limited time, Bungie Pro was free for four months with the purchase of the Legendary Map Pack.

Also, by becoming a member on Bungie.net you get eighteen free folders for a limited time to place whatever you want in them.