Several years ago, I created a bunch of maps using some map editor (I forgot the name, I've tried all the mapeditors I remembered, but I didn't find the one I was using).

Whatever it was, it had:
*Fine grained terrain control, like SCMDraft
*(trigger editor similar to scmdraft ?????)
*support for placing all units (including comsat, unknown, and the crash sc units)
*support for stacking and overlapping units, and also placing units like minerals half way in space

I've tried everything I that I can remember/find a download for, none of these editors can open one of my sample files without deleting misplaced units. I think that I might have been using the emerald editor, but I can't find a working link for that.

Anyway, does anyone know what this might have been, or know of any other good map editor (with a download link, if possible) that supports these features?

Wrong forum. However, SCMDraft can do all of those things you listed.

What is the right forum?

anyway, SCMDraft can't seem to do overlapping/space placement very well.

Units in this map are getting deleted.

That's because you aren't utilizing all of the features it provides. The right forum is UMS Assistance, I believe.

I bet it was emerald placer.

X-Tra Edit?
But quite possibly it is the Emerald Patch.