If you have some coding skills (C# or Visual Basic.NET for example), Google has released the Google Deskbar API.
Google Blogoscope mentions a few of the things could do with it:
+ Locate and play a music play list on your hard drive.
+ Solve algebraic equations.
+ Send instant messages.
We blogged an item about three weeks ago about the Deskbar “graduating” for Google Labs.
Remember, the Google Deskbar and Google Desktop Search are two different applications.