TNT: Evilution (TNT.WAD)

As you likely know, TNT's Evilution began its existence as a freeware megaWAD developed by Team TNT, who had its origins in a certain Doom mailing list. A bunch of people poured their hearts and souls into the mapset, and just as it was supposed to be released, John Romero popped in, asking if id could buy it, to be published as a commercial work. TNT agreed; thus began a rigorous playtesting / polishing session that delayed the release of Evilution until after TNT put out their freeware sequel, the illustrious Icarus: Alien Vanguard. Nowadays you can find Evilution as part of the Final Doom package alongside The Plutonia Experiment (which is kind of a TNT project, in that the Casalis were members of Team TNT).

Hell to Pay (HELL2PAY.WAD)

Hell to Pay is the other half of WizardWorks' WAD combo, crafted by Jimmy "EvilGenius" Sieben (who was also a major contributor on TeamTNT), Mackey "Avatar" McCandlish, and Jim Elson. It's a full replacement for Doom II, replacing all 32 maps, and a partial conversion, replacing the sprites of several weapons and more than a few enemies, using primitive 3D renders for the imp, demon / spectre, cacodemon, mancubus, pain elemental and lost soul. They also have a host of new sounds to go along with the mechanical enemies resulting in some gaffes; the mechanized sounds replace some of the generic demon noises which are shared by the upper-class demons.

Perdition's Gate (PERDGATE.WAD)

Perdition's Gate was one of a suite of Doom commercial WADs published by WizardWorks. The project started out between Tom Mustaine and his father, Bob, as a third megaWAD for inclusion with Final Doom, but at some point "the Final Doom window of opportunity had closed", so they took the project over to Wraith Corporation. Composed of some prominent members of the community (notably Jim Elson, Jimmy "EvilGenius" Sieben and Mackey "Avatar" McCandlish), they were producing a megaWAD that wasn't being released by id, Hell to Pay. Wraith Corp. helped finish out the rest of the megaWAD, giving the community another pair of commercial products, roughly analogous to Final Doom.