Google Desktop was desktop search software made by Google for Linux, Mac OS X, and Microsoft Windows. The program allows text searches of a user's e-mails, computer files, music, photos, chats, Web pages viewed, and other "Google Gadgets".
In September 2011, Google announced it would discontinue a number of its products, including Google Desktop: "In the last few years, there’s been a huge shift from local to cloud-based storage and computing, as well as the integration of search and gadget functionality into most modern operating systems. People now have instant access to their data, whether online or offline. As this was the goal of Google Desktop, the product will be discontinued".
Read more about Google Desktop: Release History