DocFetcher is a free and open source desktop search application.

It runs on Windows, Mac OS X and Linux and is written in Java.

[1] The application has a graphical user interface, which is written using the Standard Widget Toolkits.

This means the program must always be running to monitor changes, but search results are instant.

Note that a commercial version of the program DocFetcher Pro is in development[4] with additional features.