http://googsystray.sourceforge.net/

"Googsystray is a system tray app for Google Voice, GMail, Google Calendar, Google Reader, and Google Wave. The idea is to be able to keep track of all that stuff without having to keep a bunch of browser tabs open, or constantly checking them. It notifies on new messages, alerts, etc., and provides basic services quickly (Reading or sending a new SMS message, or marking an email read, for example.)"