RSSTellart's NADA Mobile was launched a few months ago. Since then, the Tellart folks have released the source code under an open source license, so you can use it to build your own iPhone applications using Apple's Dashcode as your development environment:
NADA Mobile is a suite of applications, originated at Tellart in 2008, for running xhtml css javascript "sketches" of new applications. The sketches run on the iPhone/iPod Touch hardware but are even useful for prototyping things that aren't going to be iPhone apps. "Sketches" are generally built in Apple Dashcode, or just a text editor, and then uploaded to the RunSketch iPhone app using a desktop app called SketchServer.
NADA Mobile is an enhanced version of Mobile Safari that gives you access to the accelerometer, GPS, microphone--and can even be used to read the value of an external analog sensor attached to the device's mic input (without using a computer or a microcontroller).
I love the way they've integrated sensors into NADA Mobile. Like the external keyboard solution shown off by Perceptive Development in iPhone Hacks, Tellart uses the microphone in port. But instead of working with serial connections, Tellart's 1/8-inch Jack uses a simple design to read the value of variable resistors. Check out the instructions for talking to a sensor from NADA Mobile: Tutorial: Creating an Application Sketch w/ Sensor
