SLumpEd

From Doom Wiki

SLumpEd is a wxWidgets based WAD editor for various Doom engine games, created by Simon Judd (SlayeR) in 2006. Some say it resembles NWT in its interface, it can be used to add, edit, view and replace lumps inside multiple WAD files. (this is because SLumpEd has a tabbed interface, allowing the user to edit many WAD files at once, also capable of swapping lumps between said files)

It also includes many other features, such as syntax highlighting for various text-based lump formats and PK3 and ZIP file format support.