Games with level editors?

Just wondered - post xmas boredom sets in...

At the risk of sounding dumb - what is a games level editor?

Something that lets you play with the game design, save it and post it online for others to play with; new pac man levels, etc.
(answers own question)
1. There are plenty of NES level editors for Zelda, Bubble Bobble, etc, and if you make heavy use of an emulator (like me) you could post modded levels for others - but that would be illegal since it would be a modified ROM image...
2. The excellent hpc Slay has a map designer (and themes editor) but you can only play user designed maps on the PC version.
3. Conquest (the Magnodyne version, not the one by the "Slay" guy) - which is a derivative of Risk - has a fairly good map editor, and you can play the maps on 2.11, HPC 2000 and windows machines.
3. There are a couple of Sokoban clones that have editors, and I also found a Mr Digger clone that had a level editor, but it was such a weird game I couldn't follow it.
4. Kyle's Quest - ported from Palm - supposedly had a level editor, but development seems to have dried up over there, if you check the message boards, and all the links dead end....
5. ... And of course there's Doom...

Still looking.... any advice?