8 years ago I wrote an opensource dashboard for the original xbox. I was unhappy with advmenu on my mamepi box so I revived it and got it functioning as a simple game launcher for the raspberry pi.
It uses arrow keys and MAME buttons 1 and 2 for navigation and uses a simple XML configuration script. It's also themable to some degree.
There's still some xbox-related cruft to remove but I'm working on using it to power my bartop arcade now. It's got a few bugs still (slow rendering primarily) but its close.