The DOOM Hack Kit contains (6) files:

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DOOM Hack Ed
Hack the DOOM .exe.

HERETIC Hack Ed
Hack the HERETIC .exe.

midi2mus
Converts midi files to DOOM mus.

mus2midi
Converts DOOM mus files to midi.

DeuTex & DeuSF
Wad composition tools for DOOM.

Endoomer
Edit the DOOM "quit screen" text.

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More idgame1 utilities can be found at the Walnut Creek archives:
ftp://ftp.cdrom.com/pub/idgames/utils/