Halo: Out With a Whimper
From Halopedia, the Halo wiki
Halo: Out With a Whimper, abbreviated H:OWaW, is a side-scrolling fan game developed by TriBlox Game Studios. The game was cancelled sometime around 2013.  It is neither endorsed nor supported by either 343 Industries or Bungie and is thus non-canon.
The game is set around the events of Halo 2 and Halo 3 on the human mining colony Atlas as it comes under siege by the Covenant, who are looking for something hidden beneath the planet's surface. Not much else is known other than that the Flood was to make a major appearance and serve a pivotal role in the game's story.
The game centers around members of the 3rd Class of the SPARTAN II program, better known as the 2538 Project, codenamed Red Team. The following are the current members of the Red Team:
The weapons in H:OWaW vary greatly. The game features every weapon seen in Halo 3, as well as some from Halo: Reach and some custom weapons, such as the "Shredder", a Brute sniper rifle that fires explosive rounds. 
The soundtrack for H:OWaW was produced entirely by Jonathan Churchill.