RISC OS is a computer operating system designed in Cambridge, England by Acorn. First released in 1987, its origins can be traced back to the original team that developed the ARM microprocessor. RISC OS is owned by Castle Technology Ltd. You can find out more at sites such as RISCOSCode, riscos.info, The Icon Bar, risc/pi and RISCOSitory.
If you are new to RISC OS, you might want to look at the introductory pages in our wiki here.