Jack Dorsey from began Friday's procession of developers. His company's app turns the iPhone into a credit card reader, giving users the ability to accept payment via credit card using a small, self-powered plastic card reader that plugs into the iPhone's audio jack. During the live demonstration, Kawaski donated $25 to Red Cross using nothing more than Dorsey's iPhone and card reader. The process was remarkably seamless and intuitive: slide the card, enter the amount you wish to charge, sign with your finger on the touch screen, and voila. After the transaction is processed, the app sends a receipt via e-mail.

While this technology should be great with non-profits, as it would allow Red Cross workers to accept donations via credit card using only their iPhones, I'm not sure how well this will fly in the private sector. I, for one, would be wary of swiping my credit card on a stranger's iPhone--what's to keep someone from writing a card-stealing program that would allow them to repeatedly charge my credit card once they swipe it? Unless Square can offer a legitimate solution to these concerns, I doubt many people will use this app to make Craigslist purchases--an example Dorsey brought up more than once.

Next up was . His company's app effectively turns the world around you into a guided audio tour. Using your iPhone's GPS, or by simply typing in your location, Hear Planet loads up and reads information about your location to you.

It's a pretty cool idea, and the demo was impressive, with the app instantly showing a list of nearby attractions in the area that it could inform you about. Guided walking tours are also in development for this app, which could be extremely helpful for tourists in any location. is available for free; there's also a that includes native mapping integrated with the app.

came up next, to show off his company's for the Mac. His humorous presentation involved him filming Kawasaki live and adding fun headlines and various affects to the footage in real time--the first such headline reading "I am a Twitter whore." The app's purpose is to allow anyone to create their own TV show by making headlines and other fun effects easy to implement. While there aren't any post-production features, BoinxTV looks like a solid choice for on-the-fly web TV productions. BoinxTV costs $499.