A Windows Calendar
Everytime I connect remotely to a Windows system to use one of our legacy applications, I wonder why the XP team put such a useless feature on the date tray applet: how often do you need to modify your date and time, or change your timezone? And conversely, how often do you need to check a date in the past or future? This is one of the small usability things that Gnome does better, as you can see in this image.
Given that the legacy application I have to use the most is our timesheet app, some time ago I decided to look for a free calendar and after digging through quite a bit of Google search results I found the excellent (and free) Date In Tray by CrispyBytes Development. As you can see it’s just a tiny application, but when you’re checking dates it’s a real time saver.