More info available here: http://youfoundasecret.wordpress.com/...
Hey, did you know that Minh "Gooseman" Le, before he created Counter-Strike, actually made similar "tactical action" shooter mods for other games? Well, besides Action Quake 2, anyway.
A friend of mine from a community I frequent made a video of this mod, and I wanted to play through it. The mod itself comes with three levels, and you can play through the entirety of Quake (and any mods/custom levels, I assume) with this. It adds a bunch of real-life weapons like the MP5 and M16, along with selectable fire rates, and an interesting mission structure.
I really wish there were more levels, though. Even though it's probably 12-13 years old now, it's still very fun.
You can download the mod here: http://www.quaketerminus.com/addon.htm
Requires Quake to run, as well as a Source port (ProQuake, Darkplaces, etc). I used WinQuake to record this.