This one is a bit of a mystery.  I've found two references to Business BASIC on the net.  One is from the C64-Wiki that states this extension was by Kingsoft in 1985 and is also known as S'MORE Basic.  The other reference also by the C64-Wiki says "There is a module extension known as Business Basic for the C64 or the C64 Basic V3.5 implementation published in 64'er Magazin 6/90 to get BASIC 3.5 capabilities on a C64 hardware.".  I'm guessing this is the later, but since I can't read German you'll have to investigate this for yourself.