I work in the embedded world, using mainly C and no GUI at all (because there is no display screen).
Moving over to the non-embedded world, in which I have nearly no experience, what is the best programming environment (langauge/IDE/etc) for me to build a simple window-form application that will run on all the common platforms: windows/linux/mac-os ?
I do not want to build a web-app.
I have my eye on Python and one of it's widget libraries, QT or WxWidgets. Is that a good option ?
I like GTK+ personally but that or any of the ones you mentioned should be OK. I don't know which is the best in terms of least RAM usage.
Both wx and QT have embedded/universal versions where the widgets are drawn directly. They can both be called from python,but if you have a very small system python or py2exe might not be available.
I think you should try Html Application.It is something like web page it contain DHTML,java script,ActiveX but it is execute like .exe .
Edit: Sorry for advice you html application.I just know it can run on windows only.
What kind of application is it going to be? Have you considered a web-based application instead? Web-based apps can be super flexible in that sense - you can run them on any platform that has a modern browser.
Unless you want to embed HtmlWindow I'd go with wxWindows... works everywhere without problems so far for me.
Qt is a good choice to start with. In my opinion it has a best (easy to use, simple & informative) API Documentation. Package also includes many examples - from very basic to complex. And, yep, it`s truly crossplatform.
Check Qt Licensing page, the library is free only for GPL projects.
I`m using QDevelop as text editor, but there are many other alternatives - Eclipse, KDevelop, Code:Blocks, VS plugin & etc.
I have both worked with PyQt and wxPython extensively. PyQt is better designed and comes with very good UI designer so that you can quickly assemble your UI
wxPython has a very good demo and it can do pretty much anything which PyQT can do, I would anyday prefer PyQt but it may bot be free for commercial purpose but wxPython is free and is decent cross platform library.
Why not use swing and java? It is quite cross platform, and looks reasonable for form apps. If you squint a bit and ignore the java, its quite pleasant - or alternatively, use one of them dynamic languages on the JVM (Groovy http://groovy.codehaus.org/GUI+Programming+with+Groovy is my recommended one).
By far the simplest choice for creating native cross-platform applications is REALbasic. Give it a try and you'll have a working app for Mac OS X, Windows and Linux in minutes. No run-times or other stuff to worry about.