RuneScape 3 is the upcoming overhaul to the current free to play, browser based fantasy MMORPG that many older gamers grew up with as kids. Recently, developer and publisher Jagex announced that the beta for RS3 has now gone live for a group of developer approved testers and players who currently hold a paid Gold and Silver memberships.
Currently the previously announced HTML 5 version is live for testing, giving players a chance to try out the new game and assist the developer in hunting down bugs and glitches. Players looking to try out the beta can still apply for beta access at the official site.
Source: Official Announcement