At this rate it is going to take thousands of years for me to post everything here.
Many are probably aware of the excellent Q1Arena mod that transforms Quake into a Quake3 clone.
But maybe less well known are these Quake3 DM maps converted to Quake.
I have put together an unofficial update for Q1Arena that includes:
q1q3solid and q1q3monsoon as the first two Q1Arena maps.
Duplicated animation frames for rlboom.spr and s_plasma.spr to prevent error messages, replaced corrupt glboom.spr with a copy of rlboom.spr. (New animation frames would look better...)
Impressive_a.wav converted to mono.
Console background and icons taken from the Q1Arena logo.
Two demos featuring really bad game skills.
Alternative gfx.wad from Quakeworld.nu.
Remove the - to download.
Extract q1a_075.zip into your OpenQuartz drawer, then extract the update to the same place overwriting any files. If you use glQuake be sure to delete the OpenQuartz/q1a/glquake drawer before running it for the first time, otherwise it will crash. It is also worth getting hold of the other converted Quake3 maps, a couple of them will crash though...