A full programming language and environment extending the features of the venerable HP calculator programmable calculators. With XRPN you can accomplish a wide range of modern programming tasks as well as running existing HP-41 FOCAL programs directly. XRPN gives modern life to tens of thousands of old HP calculator programs and opens the possibilities to many, many more. New in 2.0: Startup speed 4X. Added command 'cmds'. 2.1: Fixed rounding overflow bug. Added : commands to access underlying Ruby. 2.2: Added error exception (flag 25) with commands 'error'=CF 25 and 'unerror'=SF 25. 2.3: Better Flag 25 handling.