David Eubank's pCAM and pCINE were great applications for the Palm OS. They helped you compute depth of field, hyperfocal distance, angle of view.... Together, they were like a computerized version of all those charts in the American Cinematographer's Manual that you always referred to on set. Now, Eubank has outdone himself with pCAM for iPhone, which combines the pCAM and pCINE applications in a new interface. If you have an iPhone and you shoot film or video, this is a supremely useful tool. At $39.99 it may seem pricey for an iPhone app, but in my opinion it's well worth the price.
pCAM for iPhone [iTunes store link]