Q4Max adds many features and fixes to Quake 4, making it a much more enjoyable and complete game. For this reason, most servers running Quake 4 are running Q4Max.
This screenshot shows the "multipov" splitscreen mode, which allows spectators to follow both players at once in a duel.
You can also watch in "picture in picture" mode, with one view smaller than the other if you prefer.
Also see the item timers on the right hand side of the hud, showing when the different armours are due to spawn again (only for the spectators, of course!)