Modifications and Add-Ons

Auto-NetHack
Version 3.4.3 configuration utility. News, usage notes, and source.
http://auto-nethack.sourceforge.net/

Bertelli's Place - NetHack Patches
For version 3.4.x: Whips, Bard, Monk Flying Kick, and Wizard Staff.
http://bertelli.name/2003/12/nethack-whips/

Jukka's NetHack Modifications and Utilities
Reclist standalone utility and a collection of version 3.4.0 patches.
http://www.netsonic.fi/~walker/nethack.html

NetHack Additions
Heck^2 patch, Abigaba tileset, and a random horribly drawn cartoon.
http://www.multifoliate.com/nh/

nethack-el
Version 3.4.1 as an emacs major mode. News, screenshot, and source.
http://www.nongnu.org/nethack-el/

PatchHack
Mild variant collecting various authors' patches.
http://patchhack.sourceforge.net/

Stan's NetHack Page
Patches, utilities, and related links.
http://nh.gmuf.com/

Unix Hearse
Utility to exchange bones files with other players for Linux and similar systems.
http://www.argon.org/~roderick/hearse/

YHACS - You Hear A Clicking Sound
Sound theme for Windows. Requirements, installation directions, and sample files.
http://xoomer.alice.it/pid/