Google Desktop 

Google Desktop makes searching your computer as easy as searching the web with Google. It's a desktop search application that provides full text search over your email, files, music, photos, chats, Gmail, web pages that you've viewed, and more. By making your computer searchable, Desktop puts your information easily within your reach and frees you from having to manually organize your files, emails and bookmarks.

Google Desktop doesn't just help you search your computer; it also helps you gather new information from the web and stay organized with gadgets and sidebar. Google Gadgets can be placed anywhere on your desktop to show you new email, weather, photos, personalized news, and more. Sidebar is a vertical bar on your desktop that helps you keep your gadgets organized.