This is a 2 physics pack that I made a while back. The first one is playable, if rather gimmicky. The second one IS NOT PLAYABLE AT ALL, EDIT and was included as an example of the variety of things you can do with this EDIT. They both involve pressing the walk key to "fly". Nofall2 is not playable because I set player gravity to a negative number when walking, but the problem is that if you're killed you just keep going up and up and up into the ceiling. Because of some unknown engine property, if you accelerate into the ceiling while dead at a constant rate, it sends you up through the ceiling, where everything looks untextured, then for about a minute of that you come up through the floor, continue upwards through the ceiling and repeat. Because your corpse is still moving, it is impossible to respawn.
There. Do what you will with this, but at least let people know what you are doing before hosting it. EDIT In response to Tim, here are some suggestions for getting the most out of this: 1) Certain maps, such as Intercontinental Divide, get the most out of this (I found quick six in general to be pretty good for it). 2) The setup of this is such that a person on the ground can usually trump a flying person. That's alright, because in my experience there's only one or two people spoiling like that. 3) You can control the rise and fall (and direction [you can build up mad speed]) by shooting in the opposite direction (preferably with a machine gun, rockets don't work as well).
All credit for concept goes to Count Roland. Other tweaks are credited to me. He has okayed this for distribution last time I saw him.
Very useless physics, the only thing I noticed was that I was running faster (wow!), and upon getting hit by some projectile I found myself floating above the map or stuck in the ground. I wouldn't recommend hosting this on a multiplayer map.