Old School RuneScape was released on February 22, 2013. This release occurred despite the fact that even though a poll used by the developers to gauge interest was to be closed on March 1st.
Old School is essentially a modified version of the game as it was on August 10 2007. Updates have been added to this version which make it different in a few key areas compared to the truly 'old school' 2007 version. Notable additions would be Nightmare Zone - a minigame in which players fight bosses from previously completed quests - and the soon-to-be-released Grand Exchange.
The addition of new content to Old School is decided by the players in developer polls. A piece of content will either be suggested by a player via one of Old School's developer QA live streams or brainstormed by the team itself. A proposal will then be created and this proposal will be polled to current players of the game. Proposed content requires a 'Yes' vote of 75% or more in order to make it into the game. Old School has a separate development team from Runescape 3 (aka EOC).