Sounds like Microsoft has finally decided to port the venerable Halo series to pc.
https://store.steampowered.com/app/976730/Halo_The_Master_Chief_Collection/
It sounds like the release will be Halo, Halo 2, Halo 3, Halo 3 ODST, Halo Reach, and Halo 4. So that's cool, but they are releasing it in an odd way. It sounds like the first game to be released will be Reach, then Halo, Halo 2, Halo 3, Halo ODST and Halo 4. It fits the chronological order of the series but you will need to buy each one individually. Right now people are saying it will be $5-$10 per game which is a pretty good price despite their age, if true. It also sounds like you might need an Xbox live account to play them, it sounds like just having one will be enough, you don't need a paid subscription.