I have written an app for the ipad. Is there a way to use the app.js instead of index.html in a desktop application?
At current, Titanium Desktop requires an HTML file—there's no way to run an app with no windows. As a workaround, you can make your initial window invisible in tiapp.xml:
<ti:app xmlns:ti='http://ti.appcelerator.org'> ... <window> <id>initial</id> <visible>false</visible> ... </window> </ti:app>
Include your app.js in that window, and you've got yourself a pretty similar setup. Just be careful to make sure you call
Titanium.App.exit()to close the application when all visible windows are closed on Windows and Linux (you may or may not want to do this on OS X since many Mac apps are designed to stay open even with no visible windows).
Although it is possible, as stated by Rob, please keep in mind, if you have any iPad specific API calls or interface objects that are not included with the Desktop API, you are going to have some problems.