See thread title.
In case you ask what zDoom is, zDoom is one of the best doom source ports. The reason is that you can look up/down, jump, and change your appearance (if you have a WAD containing a skin). And because that zDoom uses some coding from the Quake 2 source code, people can make a Dehacked file which can replace a weapon with a railgun! Heck, you can replace any weapon!