I have written a number of online applications, using either Flash, JavaScript, or HTML front ends, and a PHP backend.

PHP - ASP Convertor - converts simple scripts written in the open source PHP to Microsoft's ASP.
ABC Homeopathy - online software suggests homeopathic remedies from a database of over 64,000 symptoms and 650 remedies.
BT Better business game - though a game rather than an application, it does show Flash impersonating Windows.