Mulitasking? I suppose it not really a program just part of the OS, but I think it did influence the industry in how a OS should function. (I only say it because I think everyone else have already said the best programs)
Oh and just to be even more off topic of programs another Big Influence of the Amiga to the computer market was to have a two button mouse. In a way I'm right to post this as the industry must of seen the good users of having a two button mouse on the Amiga inside of programs, so promptly got there own, but in a way I know I'm wrong to post it
