In theory, but we don't know of anyone who has attempted this yet. Also, it doesn't have the numerical flexibility to handle scoring of hands. Very probably, Zillions has very good support for defining new pieces and new boards. In fact, we built all the chess variants included on the CD-ROM just like you would, using Zillions. From what I remember of Abalone's rules I see no reason why it couldn't be implemented.
Monopoly is a bit complicated for a few reasons.
Zillions is not designed to handle arbitrary numerical amounts that you'd need in order to handle the money. Zillions has no direct support for stacks of cards, and it would be very difficult to try to implement all the rules on all those cards. Zillions plays well in games like Checkers where it can find good tactical possibilities by looking ahead. This is a well-known syndrome of game search engines that AI researchers are currently grappling with. Email your question to Zillions Development .