Anyway, if you liked v1.0, you'll love v1.1, and if you missed v1.0, get on
the bandwagon and check out DMapEdit v1.1.
Here's a smallish chunk taken from the docs:
===== Begin included text =====
DMapEdit v1.1 - a doom map editor!
Welcome to DMapEdit. DMapEdit is a true map editor, and not just a
thing editor.
[...]
So, what all can you do with this editor? Well, it is a full featured
thing editor, so you can move things around, change them, add/delete
them, etc. Thing editing has no limitations on it. You can also edit
vertexes, adding/deleteing and moving them about as you wish. Changing
them around and saving it back to the WAD file may cause problems with
the segs, but I haven't really tested to see what will happen. It will
probably look really strange, though. You can save your new level to a
data file, however, and use it with version 2.0 when available, too
finish your 'great new world'. Alternatively, you can save it to a
PWAD (also known as a 'working wad file'). It really doesn't matter
which method you use, however, DMapEdit is probably the only program on
this planet that can use it's datafiles, so save it to a PWAD if you
want to use a map with another editor.
You can also edit lines and sidedefs, adding/deleting and changing them.
Sector editing has also been put in now, allowing you to edit this
information now too. This covers basically all the editable values on a
map. What's still left to come is automatic structure building
routines, to make the blockmap, nodes, segments, and sub sectors.
===== End included text =====