Excalibur is described as 'for Windows 32-bit version is a freeware full featured RPN-only calculator. This is a serious calculator for serious users' and is an app in the Education & Reference category. There are more than 10 alternatives to Excalibur for a variety of platforms, including Windows, Mac, Android, iPad and iPhone. The best alternative is Windows Calculator, which is both free and Open Source. Other great apps like Excalibur are Numi (Freemium), PCalc (Paid), Caligator (Free, Open Source) and XCALC (Free, Open Source).