treebeard is from the new owner of CSTAL.
i doubt treebeard is stronger than cstal.
on the other hand they claim that treebeard is used by MSN chess.
i never heard about this (MSN ? is that some kind of orcus in the web?)
and visited the place.
visiting MSN chess was a very irritating experience. it felt a little like the makers were under drugs.
there is also this tournament chess II at amazon.
the 2 reviews by customers say:
Game plays well enough but has major flaws - black castles through check and in some modes the computer crashes. It requires a minimum of nine menu selections just to begin playing the first game and seven to play the next game. Graphics are OK but lost a lot of games because black pieces are the same color as the table background and there is little discernable difference between a bishop and a pawn. Don't turn off the lights (a feature of the program) because the screen will be black and unless you can find the switch again you're in real trouble. Restarting displays the same black screen. In all fairness there are lots of various features and although it plays well enough it is incredibly irritating to click through nine menus every time it's used.
that sounds more like a toy program. i doubt it has anything to do with CSTAL that was a serious chess program.