* It can build apps for Windows, Mac OS X, Linux, Android and iOS.
* It has a web engine similar to PHP that allows to use HyperCard like language mixed with HTML code.
* LiveCode authoring environment runs on Mac OS X, Windows and Linux. Older versions run on Mac OS Classic as well and can generate powerPC code.
* They are working on HTML5 deployment.
* The language is dual licensed. You can have the GPL community edition for free with source and/or a commercial edition.
* Its one of the best development community out there. They've been doing this for decades and are very friendly.
The challenge for LiveCode is that in the intervening years, of course the complexity of the system has gone through the roof. I think HC represented a conscious choice to limit its own feature set in order to make it presentable to novices, which opened it up to criticism from commercial programmers who thought it was a toy.
I honestly don't know how to create a tool that satisfies the pro's without blowing away beginners and hobbyists. Possibly the magic of Python is that the basic package simply doesn't come with any advanced features (they are installed as packages), allowing for an uncluttered learning environment.
Oh, I didn't know that they went open source. That's cool.