Of the somewhat handy tools we could talk about the calendar, which lets you save notes and events on any day. FlashTray also has a nice feature in the Window Sizer. This lets you create custom sizes for your different application windows. The Character Map is also somewhat handy to copy and paste characters. It offers loads of ASCII and Unicode characters.
In all, FlashTray has a few somewhat useful features, but it's not original enough to become an indispensable application in your task bar.