Here is the github page for the source code including the kernel, board support packages, and sample applications: Github.
This video demos how Stratify OS and the Stratify App can be used to build a customized GUI.
The following video shows how to install StratifyOS on the Nucleo-F446ZE board. The bootloader, OS, and HelloWorld can all be installed in less than one minute and in just a few clicks!
I just posted a new video of the upcoming Stratify App which will allow you to build a customized UI on desktop or mobile for any Stratify OS hardware.