From code.google.com:
[...], Google launched Google Sitemaps, a new service designed for webmasters that enables them to automatically submit their web pages to Google. It is meant to provide Google with more information about web content so we can improve search results for users worldwide. As part of this launch, we’re releasing Sitemap Generator, an open source tool that generates an XML sitemap for a few simple use cases and thus shows developers how to create these files programmatically.