Gundams and Halos is an ASB timeline by Pkmatrix in the chronological list style which crosses over various Gundam universes with the Halo franchise. The timeline has gone to some length presenting a universe that mixes elements of both while also trying to maintain a sense of continuity with the present day world, leading up to the inevitable first contact between the Human race and the Covenant. It was first posted in March 2013 and as of June 2013 covers the period from 2011 through 2496.
It can be read here.
The timeline covers a wide range of locations across several star systems:
The timeline begins and splits off from OTL in September 2011 when scientists at CERN in Switzerland and LNGS in Italy observe Neutrinos passing through Slipspace, proof that faster-than-light travel is possible, but erroneously determine that their instruments are faulty.
From that point forward, the timeline becomes a mix of elements from Gundam's Universal Century, Gundam's Cosmic Era, and Gundam's After Colony era while using the background of Gundam 00 as the skeleton. There is a second Point of Diversion in April 2301 which butterflies away the events of Gundam 00 itself, after which elements of Halo become more and more prominent.