If you are looking for PHP 4/5 classes to access Google Data APIs, here is a good library including classes to :
- Handle account authentication APIs.
- GData APIs.
- Google Calendar Data API specific class.
- Blogger Data API specific class.
The list of Available Google APIs, is becoming pretty huge, but there is already codes for Maps API for example. That’s all what you need to create killer mashups, just use your imagination and some AJAX 🙂