Create Invoices from your Google Calendar

gTime creates simple invoices by reading from your Google Calendar.  There are screenshots of creating an invoice on the project hosted at Google Code. 

The project was a birthday gift for my wife last year, but it was also a hobby project to explore Google App Engine and GData APIs.  The primary motivations for the app were to:

1. eliminate redundant data entry by generating invoices directly from the appointments you already keep current on your Calendar. 
2. work with any Calendar client by reading billing rates from plain text in the calendar entries themselves.
3. protect client confidentiality by printing Web-based invoices that do not pass identifying name and addresses over the Internet.

That last goal is a bit specific to healthcare providers, but expand the app for your own needs (and maybe even punch out a few features on the wish list)