building cross platform apps - environment and SDKs

A web server:
XAMPP - http://www.apachefriends.org/zh_tw/xampp.html

Sencha touch 2 framework:
http://www.sencha.com/products/touch/

IDE for html/javascript/...etc
http://www.aptana.com/



Download those files, then you can begin to write the cross-platform apps using javascript and html5.

cheers