There are many toolkits to use. It depends on the type of app you're writing and who's going to use it and what platform its for. Is it mainly for Windows user

There are many toolkits to use. It depends on the type of app you're writing and who's going to use it and what platform its for. Is it mainly for Windows users? Might want to go with .NET. There are free versions of Visual Studio available for this purpose. Is it for Linux systems? GTK with C/Python or Qt with C++/Python maybe a better option. All the libraries and compilers are free. Mono (an open source .NET implementation) also works well on Linux. If its for the Mac then Objective-C + Cocoa is the de facto method. The IDE, Xcode is a free download from Apple. You can also get python bindings for Objective-C. If it has to run on many platforms then you might want to think of a cross-platform toolkit. If the program has a very simple UI, then you can probably get away with using wxWidgets or QT with Python. If UI is more involved, then you will probably want to write the front-end for each in it's own native framework.