VisionMobile has done extensive research (97 pages) on this in their Cross-Platform Tools 2012 report. It's available for free after registration. They've found over a 100 different tools and written detailed profiles of the 15 major players. Those are:
- Adobe PhoneGap (Apache Cordova) - JS apps with HTML/CSS/JS UI inside a webview
- Adobe Air / Flex -
- Ansca Corona
- Appcelerator Titanium - write JS instead of instead of Obj-C or Java, Titanium did the webview thing similar to Phonegap in older versions
- Seregon DragonRad
- IBM Worklight - basically a commercial enterprise version of Phonegap
- Ideaworks 3D Marmalade
- MoSync
- Rhodes and Motorola Solutions RhoMobile - Ruby with webview
- NetBiscuits BiscuitML
- RunRev LiveCode
- Digia Qt
- Sencha Touch - JS/CSS UI framework
- Unity - game engine, probably not what you're looking for
- Xamarin MonoTouch and Mono for Android - write C# instead of Obj-C or Java
I'm looking into this currently for Ruby on Rails shop that wants a mobile app as well. We're looking at Rhodes but also at RubyMotion, Ruboto and MobiRuby, which instead of webviews allow Ruby to be used to code the UI instead of Objective-C or Java.
Whether you want a webview-based solutions or nod depends on your requirements and the used UI framework, such as jQuery Mobile, Sencha Touch, Zepto, etc etc. Facebook famously dropped webview (because it was slow and buggy) in favor of 100% native apps, but Sencha showed it could be done properly with their framework.
And depending on the used tool, it may or may not have the ability to write platform native code and/or UI if the framework doesn't offer the needed capabilities. Suffice it to say that there are many roads leading to Rome, and each roadmaker has its own way of doing things :)