RISC OS is a high performance and low footprint operating system. It provides a modern desktop interface coupled with easy access to programming, hardware and connectivity.  It continues to incorporate the world-renowned programming language, BBC BASIC, and is incredibly compact, fitting onto a tiny 16MB SD card. Originally developed in Cambridge, England, by Acorn Computers in 1987, RISC OS was specifically designed to work hand-in-hand with the ARM series of microprocessors.
I personally have been using RISC OS since version 3 on an A5000 system. It was the first operating system I had used with a graphical interface and it very naturally felt right as you used it. The process of learning the system was incredibly easy and even after a few hours you began to realise just how much you could do. The A5000 system with the then standard set of software, enabled the user to produce output with superfluous ease.