YouTube video courtesy of Rhomobile
Rhomobile has an interesting cross-mobile-platform development product based on the Ruby programming language. The Ruby bytecode produced in their development environment can be run on Android, BlackBerry, iPhone, Symbian, and Windows Mobile phones.
Using it for developing commercial applications requires a $500 per app license for unlimited users. It appears, however, that any Ruby developer can download their product to try it out. So, the barrier to try it is zero.
Their Rhodees Debugger (running on a Mac in the video demo above) looks very interesting. If development time can be reduced significantly compared to, for example, writing an iPhone app in Objective C, the $500 commercial license may be well worth its cost per app.