ZunTzu is described as 'tool that allows you to play boardgames and wargames live with your friends over the Internet. See the FAQ for more info'. There are more than 10 alternatives to ZunTzu for a variety of platforms, including Online / Web-based, Windows, Mac, Linux and Android. The best alternative is Tabletop Simulator. It's not free, so if you're looking for a free alternative, you could try Board Game Arena or Yucata. Other great apps like ZunTzu are Tabletopia (Freemium), Vassal (Free, Open Source), Cyberboard (Free) and Boardgame Lab (Freemium).
Tabletop Simulator is the only simulator where you can let your aggression out by flipping the table! There are no rules to follow: just you, a physics sandbox, and your friends. Make your own games and play how YOU want! Unlimited gaming possibilities!
With Board Game Arena you can play board games online with the whole world. It is a next generation game platform which makes online gaming simpler and more attractive: -- Nothing to install: play straight from your browser, from anywhere, at anytime.
Vassal is a game engine for building and playing online adaptations of board games and card games. Play live on the Internet or by email. Vassal runs on all platforms, and is free, open-source software.
The CyberBoard board gaming system makes playing board games by mail and electronic mail a more enjoyable experience. The system allows you to easily graphically design the various parts of a board game on your computer.
Battlegrounds Gaming Engine (aka BGE) is virtual tabletop software for playing boardgames, wargames, card games, and dice games, whether your players are in the same room, or on the other side of the world.