Included Gadgets are: email, weather, photos, and personalized news. Other gadgets include the clock, calendar, scratch pad, to do list and many more.
Google Desktop also allows you to search many different file types on your Mac or on the web:
text files (.txt)
email from Apple Mail and Microsoft Entourage
Microsoft Word, Excel, and PowerPoint
music and video files, including artist and song names
Address Book contacts
system preference panes
file and folder names
As with most of Googles great apps, it's free!