https://alephone.lhowon.org/
As a former Mac user I used to play the Marathon Trilogy. It was made by Bungie in the mid 90s. Back in the day we used to rocket jump and grenade hop(at significant expense to your health) in Marathon.

(pre-quake, btw)
8 peeps on a LAN. There are tons of maps and mods available for it too.
The Marathon games had:
free-look with mouse
a handful of multiplayer modes
dedicated multiplayer maps
dual-wielding of some guns
two firing modes for some guns
mods. maps, items, physics, full-on total conversions, etc
voice chat! but it did not work on PowerPC machines IIRC.
rocket jumping
viscous water/lava/sewage/etc to submerge and swim in
"film" recording (think demos in Quake)
The downside is that it is pretty old and some people complain about the controls being weird or feeling sick when playing it. YMMV. They are probably just not used to FPS games? *shrug*
It has been ages since I really spent time playing. Pretty sure I am terrible these days.

Still good fun though!
Here is a random video on youtube:
https://www.youtube.com/watch?v=1EQtYmD7Tw0
The gameplay can get pretty frantic.