WADED

WADED is a DOS-based editor. It's probably one of the first line-based editors, in the sense that you have to first draw "blank" lines on the map (they will appear purple) and then you need to select those lines, press the "Create Sector" button towards the bottom of the screen and wait for WADED to assign them automatically. One of the other good parts to WADED is that all THINGS placed on the map are given an icon. Also in addition to these other smaller features, WADED was one of the first editors to have support for Heretic.

The downside of WADED is that you have to pay 14.99$ for it.