Has anyone else heard of Installation 01? It’s a free, fan-made Halo game designed for PC (Windows, Mac, AND Linux) by Soon Studios.
It mashes together CE, 2, 3, and Reach all into one, with classic movement mechanics and everything. I’m really looking forward to it.
It has not been released yet, but the team has been working on it a lot. Updates are usually bi-weekly.
I recommend checking out the website (you won’t be disappointed):