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zDoom is a source port of Doom and Doom II that is considered very advanced. It supports Boom's editing extensions, plus all of the extensions made in the version of the Doom engine used in Hexen: Beyond Heretic, as well as several other new features.
zdoom-2-7-1.dmg (6.2 MiB / 6.5 MB)
Version 2.7.1 (2013) / DMG image
zdoom-2.8.1.dmg (6.9 MiB / 7.24 MB)
/ DMG image
Mac OS X
Emulating this? It should run fine under: SheepShaver