I know that this is really closer to software than to an actual operating system, but I call this PCF SamOS. My approach was to use the hard buttons as a means for consistent navigation, making it easy for the user to get anywhere on the remote in no more than two button presses. I've created custom graphics to give each device its own personality and vibe. I've also made use of drop-down menus in a few sections. I hope you dig it.