RISC OS was an operating system used by Acorn Computers (UK) on their products from 1987-1998. It was sold to RISCOS Ltd who released RISC OS 4 in 1999 and RISC OS 6 in 2007. Castle Technology separately released RISC OS 5 for their Iyonix computer during 2002-2008 and later R-Comp Interactive released their ARMini computer with RISC OS 5 in 2011. All versions of the operating system assume you have a 3 button mouse. The most important games were Mine Hunt by Paul LeBeau (included in OS 3.5 to 3.71) and Flag Day by Richard Hallas (included in OS 4, 5 and 6 except for 4.02).