[adrianmonk]

Fun point of trivia about XBill: you might not guess from XBill's (ahem) slick, beautiful user interface, but one of the two people who wrote XBill is Matias Duarte.

Yes, that Matias Duarte, the guy in charge of UI for Android and who came up with Material Design.

[coribuci]

There is not much of a GUI in XBill- just a bloody program with a menu and a window. The same can be said about Android - Windows 1.0 rereleased. From an engineering point of view XBill is a better achievement than the GUI of Android.