Here's a list of DOOM / DOOM II ADDONS that are not listed in the MOD / ADDON page.
DOOM BUILDER (MAP EDITOR) - <a href='http://www.doombuilder.com/' target='_blank'>http://www.doombuilder.com/</a>
SV STRIFE (PORT / ENGINE for STRIFE) - <a href='http://dsv.newdoom.com/misc.shtml' target='_blank'>http://dsv.newdoom.com/misc.shtml</a>
SEHACKED (STRIFE HACK EDITOR) - <a href='http://www.doomworld.com/sehacked/' target='_blank'>http://www.doomworld.com/sehacked/</a>
There are many others that I forgot to put here but with the time I'll be posting more... Thanks...