Years ago, after Xbox Live for the original Xbox shut down, there was a program you could run on your PC that would connect over the internet to others running that software.

It would emulate an Xbox and do matchmaking and your local/physical Xbox would see the others through the program as "local" using the system link option for multiplayer games (Halo, etc)

For the life of me I cannot remember what that was called, and my Google-fu is failing and only returning results for console emulators.

Some friends from college and I dug out our old Xboxes, and we want to setup remote play for Halo 2 and have a nostalgic "Shotguns on Midship" night.

Update: Solved. Thanks, mouse@midwest.social. XLink Kai was the software I was thinking of.