Some users were having trouble getting GTK+ dialogs to work on Mac and Linux, so I decided to create a quick solution to this problem, based on "Tiny File Dialogs" from SourceForge.net, which was licensed under zlib.
Note: currently only works on Mac and Linux. Will update the code soon, so that it will work on Windows as well, out of the box.
As you can see from the screenshots, this extension is also available for GameMaker Studio. It works the same in both.
Here's the progress I've made with the Windows version; (I can't publish it until a certain bug is fixed with MinGW):
What you see in the Windows screenshots above, was actually made with Microsoft's compiler, which is why it works in GMStudio but not ENIGMA yet.
All of pre-Studio GameMaker and GameMaker Studio's dialog functions mirrored with the *_tfg() suffix. The only functions that don't work 100% like GM are the "open" and "save as" file dialogs, which the filter argument unfinished, only one file filter can be displayed; (these problems are only present on Unix-based ports of the extension, therefore it works 100% as it should on the Windows version).
Extract that zip under this directory: