The Oberon system version corresponding to Oberon-07 (see http://www.projectoberon.net/) is not really a "GUI" and very bare-bone compared to previous Oberon system versions. Wirth mainly wanted to implement his own computer including CPU using an FPGA; to reduce his effort he left out many things from the past. You could have a look at https://github.com/rochus-keller/OberonSystem3 instead which indeed has a GUI with an Oberon based widget framework; the referenced implementation should be easy to port to your OS (see ObxPal.obx).

My taste for minimalism are a bit on the extreme side. Dusk OS isn't really about having a GUI, but graphical applications such as a PDF viewer are part of its design goals.

I was planning on not having a Desktop Environment at all and just have graphical applications use the whole screen, but I was intrigued by Viewers and Texts architecture. Their fundamental simplicity is rather elegant and I feel that mixing this with Forth's own radically simple elements, there's something quite powerful to be had. I'm not sure yet how it will materialize, but I still have that feeling.

I'm not really looking to write new graphical applications for Dusk, so I'm not planning on ever needing a Oberon-based gadget framework. The idea behind Dusk is to port existing applications onto a radically simpler platform (compared to your typical POSIX) with a minimal effort, not to write new software.

I see. In case you're interested, I also made a version of the project oberon system with a minimal, portable plattform abstraction layer, see https://github.com/rochus-keller/OberonSystem/tree/FFI. Most of the code should be compatible with your compiler.