PhoneGap

“In essence, Nitobi is building out a ‘write once, run anywhere’ platform for mobile application development… One of the co-creators of PhoneGap said, ‘The idea is you write one code base and it should work smoothly on all devices.'”

– eWeek. Read more >

obviously, this one is the thing!

Sencha – Sencha Touch Overview – HTML5 Mobile App Framework

The World’s Best Devices

Sencha Touch is a cross-platform library aimed at next generation, touch enabled, devices. Our initial beta is compatible with iOS and Android, which together represent over 90% of current US mobile traffic. Android developers can also make use of a special theme we’ve created just for Android. With the ever-rising number of Android devices and the widespread popularity of WebKit on mobile systems, we expect our supported device list to grow very rapidly.