OpenChess

D-Fend Reloaded is a graphical environment for DOSBox. DOSBox emulates a complete computer including the DOS commandline and allows to run nearly all old DOS based games on modern hardware with any of the newer Windows versions.

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http://dfendreloaded.sourceforge.net/

This is a super download. While MS Virtual PC runs your DOS chess software a lot faster than D-Fend Reloaded the latter is a lot more user friendly regarding installation, running programs and without all the typical Windows 98 hassles.

Added Zarkov 2.5, Zarkov 2.6 Socrates 3.0, Rebel 12 to my oldies collection.

http://www.top-5000.nl/cp.htm
http://www.top-5000.nl/rebel.htm

Speaking of crusty old DOS chess programs:
http://cd.textfiles.com/swinnund/disk1/FILES/CHESS/

EdChess is a personal favorite of mine. We had many a battle, way back in the day.
I had an amber monitor and a Hercules video card, so the screen was a pretty golden color.
I actually played (essentially) correspondence chess against it because I made one move per day. (Set think time to 23:59:59)
At the time, I thought I was giving the program the best chance possible but now that I understand how computers play chess I realize that I was instead giving myself the best chance possible.

I just ran EdChess 230 in D-Fend Reloaded 1.3, and it looks a bit different with CGA emulation instead of running on the Herc.
Seems to work just fine.

I use D-Fend for Psion Chess, 1985. One of the toughest old engines. A very good challenge. I'm pretty sure it was world champ in 1987 or somewhere around there. These old engines are the best sparring partners, much better than the new ones. They can actually be beat playing real chess, not just anti computer chess.