and melee attacks, as well as grenades. Bungie referred to the "weapons-grenades-melee" format as the "Golden Triangle of Halo". The player's health is measured in both hit points and a perpetually recharging energy shield. Released for the Xbox in November 2001, Windows and Mac OS X ports were later developed by Gearbox Software, and released in 2003. A stand-alone expansion, entitled Halo: Custom Edition, was released as a Windows exclusive, and allowed players to create custom content for the game. The success of the game led to a sequel, Halo 2, which was announced on August 8, 2002, at Microsoft's X02 press event. It featured improved graphics, new weapons and enemies, and a multiplayer mode on Xbox Live. Halo 2 was released on the Xbox on November 9, 2004, and later for Windows Vista on May 17, 2007. The game was released in two different editions: a standard edition with just the game disc and traditional Xbox packaging; and the Collector's Edition with a specially designed aluminum case, along with an additional bonus DVD, extra booklet, and slightly different user manual. Halo 2 introduced new gameplay elements, chief among them the ability to hold and fire two weapons simultaneously, known as "dual-wielding". Unlike its predecessor, Halo 2 fully supported online multiplayer via Xbox LIVE. The game uses "matchmaking" to facilitate joining online matches by grouping players looking for certain types of games. This was a change from the more traditional "server list" approach, which was used to find matches in online games at this time. Halo 3 was announced at the 2006 Electronic Entertainment Expo. It utilized a proprietary, in-house graphics engine, and employed advanced graphics technologies. Halo 3 is the final game in the original Halo trilogy, ending the story arc begun in Halo: Combat Evolved. The game was released on the Xbox 360 on September 25, 2007. It adds to the series vehicles, weapons, and a class of items called equipment. The game also includes a limited map-editing tool, known as the Forge, which allows players to insert game objects, such as weapons and vehicles, into existing multiplayer map geometry. Players can save a recording of their gameplay sessions, and view them as video, from any angle. Following Halo 3s release, Bungie became an independent company once more. They created two more Halo games as part of their deal with Microsoft: a side story Halo 3: ODST (2009),