Cancelled Certain Affinity Halo game
From Halopedia, the Halo wiki
Around 2007-2009, game development studio Certain Affinity were in talks with 343 Industries to produce a Halo game. The game was intended by 343 Industries to be a digital download game, and Certain Affinity pitched a number of ideas including one that had multiple people "super excited". Ultimately, the contract was close to being in place to begin development, though fell through once the then-upcoming Halo Waypoint project became a larger priority. Although the project fell through, the negotiations allowed Certain Affinity to keep in contact with Microsoft, ultimately going on to produce Waypoint and the Defiant and Anniversary DLCs for Halo: Reach, alongside continued work on future Halo games.
Some of the ideas pitched by Certain Affinity were described by studio head Max Hoberman as "a little too out of left field, a little too casual", ultimately contributing to a more serious plan closer to existing Halo games. As of 2015, one of the ideas pitched for the Certain Affinity game project is something Hoberman is still "dying to make".