RS3 is the new version of Runescape they're releasing in a few days. It has updated graphics, interfaces and the lore story line is going to turn in a new direction.
Oldschool Runescape (2007scape) is basically what Runescape Classic was for RS2 way back when. It's a copy of the game from 2007 that they restored and activated because the community voted for it. Every member has access to it for free and you get a brand new character when you start. Your log in info and display name remain, but you start off as a new account. Level 3, tutorial island, the works. For the past few weeks, they've been dropping the rare items in random locations around the map. These drops aren't occurring in the regular version of the game.