reQuiem is a custom OpenGL Quake engine for Windows and Linux. It's designed for maximum compatibility with all things Quake - past, present and future. It's fast, reliable, and easy to configure. In short: it fixes what was broken, improves what needed improving, and leaves the rest alone.
Download reQuiem for Windows and Linux. And check out the project at GitHub. Here is a better working but very beta and not meant for archival zip: http://chunk.io/f/d0bf59d08b5c4d8692ad30df8b7e9bb6
The readme says
expanded limits (edicts, models, lightmaps)
mp3 and ogg music
playback of demos from FitzQuake 0.85, aguirRe's engines, and QW
demo pause, rewind, fast-forward and quick-seek
dzip and zip/pk3; also compression of recorded demos
Nehahra, -quoth, and multiple -game arguments
md2 and md3
console tab-completion for cvars, commands, and filenames (maps, demos, sky, etc)
Options menu containing most useful settings, intuitively grouped
support for non-US keyboard layouts
But it also features
Automatic detection of limit-breaking maps. Switching to protocol 10002 when needed.
Fast and convenient video capture support. Just type "capturedemo demoname" and it will output an uncompressed AVI file of the same name. You can specify things like the framerate or resolution.
Pasting your clipboard into the console
Detects the fish count bug and fixes it internally.
MH's beautiful sky rendering
Compatibility options like "ignore the case of filenames",
built-in reverse weapon cycling: if a custom progs.dat doesn't have impulse 12/CycleWeaponReverse functionality, reQuiem can provide it.
client-side support for the new Fitz protocol (including demo playback)
screenshots taken while a map is open now get named after the map
all data from Quake Pre-Release/0.8/beta3 works
Runs on Linux and Windows. On Linux it uses OSS, with FMOD for the music.