'Xbill is also a colloquial abbreviation for Crossbill.XBill is an arcade style game for the X Window System. It was very popular among Linux gamers at the end of the 1990s, beating out Quake, though not Quake II, as Linux Journal reader's favourite Linux game in 1999.Written by Brian Wellington and Matias Duarte, the game features a bespectacled character known as "Bill".