Spotlight does Math (but not conversions)
Mac OS X has Spotlight (Cmd-Space) which rocks for not just finding files but launching applications (just start typing the name). I just discovered it also does math, just like google. For example, try typing in 5*9+pow(sqrt(10),3) . Nifty.
Alas it doesn’t do currency conversion or unit conversions. Maybe in 10.6…?