At this time, only Firefox 3.5+ . Unfortunatly Internet Explorer, Chromium, Safari, and Opera do not support enough MathML to be functional. Hopefully this will change as MathML is now part of the HTML5 spec. For best results use Firefox 4.
Wise tries to load the STIX webfonts in your browser but web fonts are only supported in fairly recent version of Firefox. To get best results you may need install the STIX fonts locally.
At the moment Wise is in its infancy and is little more than a toy that can do some basic algebraic manipulations. The goal of the project is not to create another computer algebra system, Sage already satifies this need quite well.
Wise differs from a computer algebra systems in that it does not have a REPL loop and is not a programming language unto itself. It is merely a system manipulating abstract symbols which model mathematical constructions.
Maybe, all the libraries Wise is based on can be run on Windows but I have not tested this. The primary hurdle would be getting Pure compiled and getting the Python virtualenv set up. My target operating systems are Linux/BSD and Mac OSX to a lesser degree.