MPCalcRB is a multi-precision RPN scientific calculator for Mac OS X, Linux, and Windows. It can handle numbers with up to 30,000 digits. It can also handle numbers whose absolute values lie between about 10^-40000000 and 10^+40000000. The popup menu selects from three keypads. There are keyboard equivalents for the functions and scientific functions are available including help menu which describes them. MPCalcRB was programmed with Real Studio using my MPCalc plugin and is based on my multiprecision engine fp.