The best ideas really are the simplest ones. I don't want to carry around a 17-inch notebook (does anyone?) and I'm not an accountant, but sometimes I miss the numberpad, like when I'm dropping in a credit card number or doing a stupid Excel spreadsheet, and using two hands to pound digits is just annoying next to the numpad's one-handed zen. Enter numberkey, an iPhone app that turns it into an ad hoc wireless numberpad for your Mac using Wi-Fi. There's a small desktop client that goes with it, but it's all only $1.99. And it comes with four skins to cover every style of modern Mac keyboards to keep even the most OCD weirdos happy. [iTunes via technabob]

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