I needed an easy way to set timers on my desktop PC. All I really want is to set a countdown in hours, minutes and seconds, and have it alert me when that time has elapsed. I couldn't find anything simple with some exceptions that wouldn't compile (anymore) due to missing libs (which weren't available in Xubuntu). So I whipped up my own.
You can download it from its home page, and here's a screenshot of the thing:
Additionally, I was quite amazed at how easy it is to write GUI applications using just GTK in combination with Glade. Writing this tool took me only about an hour, with no previous knowledge. All it really required was creating a GTK Status Icon with an active signal handler. The handler pops up an interface put together in Glade by loading the gcountdown.glade file using gtk.glade.XML(). Connecting signals to the widgets is also super easy with signal_autoconnect().
Take a look at the source code. It's only a measly 136 lines.