Overseeer is unfortunately dead.
However
It still works. Yes, it does take some work, especially if you want to use symbols that they didn't do. It does limit you but it also creates the 3D image.
I toyed with the idea of using NWN or Dungeon Siege to create a 3D map. However, it is a LOT of work! It gets worse, imo, when you are trying to convert something from an existing map because now you have to do twice as much work!
However, I am biased because I use CC2 and like that this program converts my maps for me, instead of me needing to do more work.
Having said all of that, I would gladly support a company that wanted to create a new version of RO!
I know this didn't help you find something new. I think that's because I haven't seen any better choices. That's just me, though.
Have a good one! Take care!
edg