a low latency kernel (whatever that means. I’ll get there to figure it out eventually)

It’s a kernel with real-time process scheduling enabled by default.

In normal kernels a process can theoretically block all other processes from running for up to several seconds, which is obviously bad for time sensitive things like audio recordings or controlling a CNC-machine for example.

In real-time scheduling all processes are guaranteed time slices in more regular intervals. This is good for time sensitive things like audio recording, but since there is some scheduling overhead it’s bad for single resource intensive processes or process trees like video games.

You can read more about the difference between a real time and low latency kernel here: https://help.ubuntu.com/community/UbuntuStudio/RealTimeKernel

Not familiar enough with this particular project to know, but a quick glance at the commit log shows some overlap in commit authors, so I guess there is at least some level of sharing happening, probably just not through merges.

But being familiar with this kind of project in general, the branches will probably never be fully merged even in the future, just doesn’t make much sense because they are server software targeting very different versions of a game client. There are also two other branches, but they “only” diverged by like one or two thousand commits so far.