Megawad

A megawad is a fan-made PWAD that, according to the idgames archive definition, contains 15 or more levels, or nears the size of a commercial or registered IWAD.

A megawad may be the effort of one person, such as Gwyn Williams' Vile Flesh megawad, or of several people, such as the Doomworld community megawad project Community Chest 2. Whether a solo or group effort, high quality megawads require a huge time investment and can take months or years to create. A megawad may well represent a Doom mapper's collective lifetime works, such as Jan Van der Veken's Classic Episode, which is mostly a collection of levels previously released as standalone WADs.

Because creating a megawad is such a massive undertaking, quality megawads are few and far between. However, they are almost always the most anticipated PWAD releases, as well as the best remembered. Megawads can sometimes exceed the size of commercial and registered IWADs, but surely they are well over the size of the shareware IWAD.

Episode replacement
An episode replacement (or simply episode) is a set of fan-made levels containing a similar amount of levels as an episode of the game the episode replacement was made for. Therefore, most episode replacements include eight or nine levels, which is comparable to original Doom's episode structure of seven normal levels, a boss level, and a secret level.

Full game replacement

 * 2002 A Doom Odyssey
 * Chex Quest 3, though it is mainly marketed as a 3rd party IWAD.
 * Doom the Way id Did

Episode replacement

 * Knee-Deep in ZDoom
 * Phobos: Anomaly Reborn

Full game replacement

 * 10 Sectors
 * Alien Vendetta
 * Claustrophobia 1024
 * Community Chest
 * Community Chest 2
 * Community Chest 3
 * Congestion 1024
 * Cyberdreams
 * Doom II the Way id Did
 * Eternal Doom
 * GothicDM
 * Hell Revealed
 * Hell Revealed 2
 * Icarus: Alien Vanguard
 * Memento Mori
 * Memento Mori II
 * NeoDoom
 * Newdoom Community Project
 * Newdoom Community Project II
 * Plutonia 2
 * Prayers Of Armageddon
 * Realm of Chaos
 * Requiem
 * Scythe
 * Scythe 2
 * Speed of Doom
 * Whispers of Satan
 * ZPack - Random Maps for ZDoom

Episode replacement

 * Dark 7
 * The Darkening
 * The Darkening Episode 2
 * Vanguard