Individuals may have strong opinions about the merits of Apple iPhone versus Google Android versus the struggling Palm WebOS versus the not-yet Windows Phone 7; but sit them round a table to discuss app strategy and those diverse platforms change from a debating point to a problem. Presuming a web app won’t cut it, how do you target all those devices without the unreasonable expense and complication of managing multiple projects? The native languages are all different; Objective-C for iPhone and iPad, Java for Android and RIM BlackBerry, JavaScript for WebOS, C# for Windows Phone 7.

There are three possibilities that come to mind. One is that all the platforms will eventually allow you to write in C or C++, making this the unifying language, though you still have some fancy footwork to do overcoming library differences. Android now allows this via the NDK, and Palm via the PDK. There is currently no alternative to Java for Blackberry, and Microsoft says native code won’t be possible on Windows Phone 7, but well, you never know.

The second is Adobe Flash. This is an interesting one, because Apple prohibits Flash on the iPhone, but Adobe has a Packager for iPhone that builds native iPhone apps from Flash projects. Another issue is that although Flash is available or promised for all the main non-Apple devices – Apple’s gift of a selling point to its rivals – it is not Flash alone that does what it needed, but AIR, the “desktop” or out-of-browser runtime. This has been previewed for Android and promised for other devices including Blackberry. AIR for Windows Phone 7? Maybe, though I’ve not seen it mentioned.

A third idea is a clever framework that does the necessary cross-compilation under the covers. This cannot depend on deploying a runtime, nor compiling to native code, because these approaches are blocked by some mobile platforms. Rhomobile has the Rhodes framework, where you code your app in HTML and Ruby and compile for devices including iPhone, Windows Mobile, RIM Blackberry, Symbian, and Android. Rhodes includes an MVC (Model View Controller) framework and an ORM (Object Relational Mapper) to wrap database access. There is also a RhoSync server component to enable offline data with synchronisation back to the server when reconnected; and the RhoHub hosted IDE for buildings apps with a web browser.

Rhomobile tells me that Palm WebOS support is in the works. They also promise Windows Phone 7 support, which intrigued me because Rhodes says it compiles to “true native device applications”. Has Rhomobile gotten round Microsoft’s opposition to native code? Apparently not; VP Rob McMillen eventually told me that this will mean a .NET IL (intermediate language) implementation.

The Rhomobile approach reminds me of AppForge, a company which produced the well-regarded Crossfire add-on for Visual Studio and compiled Visual Basic to a wide variety of mobile platforms. Unfortunately AppForge was acquired by Oracle, and its new owners showed callous disregard for existing customers. Not only did development cease; it also became impossible to renew existing licenses. Thanks to an activation component, that also blocked new deployment of existing applications – every developer’s nightmare.

That said, there is no activation requirement for Rhodes that I know of, and the framework is open source, so I don’t mean to suggest it will suffer a similar fate.

What about Java? On the face of it, Java should be ideal, since multi-device support is what it was designed for. It is a measure of how far Java has fallen that we hear far more about the lack of Flash on the iPhone, than the lack of Java. Microsoft says yes to Flash on Windows Phone 7, though not on first release, but nothing about Java.

Java as a mobile runtime needs a strong dose of lobbying and evangelism from its new stewards Oracle if it is not to fall by the wayside in this context. Hmm, AppForge.