Intuit has released a new Web application, SnapTax, that allows users to file their taxes online. SnapTax's single screen flow makes use of iframes and DHTML to provide “line-by-line help when you need it”.
The form also calculates your tax and refund after you complete each step and automatically updates your totals. I’m fairly certain this processing happens on the server. In which case the application might be a nice example of using Remote Scripting to allow Javascript to talk to a remote server from an already loaded Web page.
They’ve also done a nice job with modal dialogs effectively “graying out” the rest of the screen with a textured semi-transparent GIFF graphic repeated inside a DHTML layer. According to the site, SnapTax requires Microsoft Internet Explorer 6.0 (or higher) or Firefox 1.0 (or higher) to run correctly.
UPDATE: "Pretty much all the tax calculations are done on the client with JavaScript. The Canadian version, however, does communicate with the server every time you change a number." Thanks for the clarification!