I have been looking for a Linux system tray application to notify me of new mail on my GMail account. Unfortunately, all the notifiers I found either did not run on Linux, or had dependencies I was unable to meet on my machine (because I lack system administrator privileges). This is why I wrote LGMTray, a very basic GMail notifier, with very few dependencies.
LGMTray is implemented in C++, and only depends on libcurl (for opening secure connections to the GMail server), LibXML2 (for parsing the GMail feed), and libxpm (for rendering the icons). It uses the FreeDesktop.org System Tray Specification to dock the application to the system tray, and uses Xlib directly for all the graphical functions (drawing the icons, communicating with the tray, …). It is currently very limited in features, but will probably evolve in the future (depending on personal and other people’s interest).