The app doesn't look half bad. Kinda limited, and only looks like it supports Novak's motors, but it's a start.
Someone here (can't remember who) made an R/C calc as well. But I think it was for the Android IIRC.
I personally hate making something for one platform, whether it's for Apple, Android, Blackberry, Windows, Mac, Linux, etc. This is where web-apps shine; they are cross-platform, provided the programmer does it right.
It's ok but it's only novak motors and speedos to use as input, even on the custom setting. Still like Brian's better cause I can put all my own data in and even get a speed vs gearing chart. It is nice that the novak one gives a gearing recomendation for your setup though