PrBoom

PrBoom, short for Proff Boom, is a source port for Windows and Linux based on LxDoom and MBF. PrBoom uses the Simple Directmedia Layer library to abstract away OS/platform specifics. It therefore supports a very large variety of platforms. It was first developed by Florian "Proff" Schulze and is currently maintained by Colin "cph" Phipps.

PrBoom's flagship feature is its accurate compatibility with vanilla Doom demos. Currently it plays back almost every vanilla demo flawlessly. In addition PrBoom emulates vanilla Doom accurately, making it a good choice for anyone who wants Doom to look, play and feel like the vanilla engine did.

PrBoom+
In addition to the official PrBoom versions, Andrey Budko has further developed PrBoom on his own and released his work as an unofficial version of it. His version (called PrBoom+) features, among other things, an uncapped framerate and a chasecam for demo playbacks. PrBoom+ doesn't compile in POSIX environments.

Demo recording
PrBoom's Vanilla Doom compatibility means that it is possible to record Doom 1.9 demos in PrBoom. However, demos recorded with PrBoom are given a "watermark" which makes it possible to identify them. This is due to the Compet-N rules which require demos to be recorded in Vanilla Doom. In particular, PrBoom includes features which would make it possible to "cheat" by using savestates to record demos in several stages.