There seem to be some more dev kits being made available Mark II Update - January 2021 - #18 by gez-mycroft
But if you already have a Raspberry Pi 4 + LCD Screen you could try out https://community.openconversational.ai/t/mycroftos-a-bare-minimal-production-type-of-os-based-on-buildroot/ tho the latest image is in a pre development state
Skills on the Mark 2 do not have their own window but run inside mycroft-gui GitHub - MycroftAI/mycroft-gui: The Graphical User Interface used by the Mycroft Mark II and more, Skills consist of a QML UI with all the skill logic from the Python skill, Mycroft-gui along with Mycroft-core can also be installed on any latest Linux distribution if one want to develop on any system, you can read more about developing your own skills with a UI here Displaying information - Mycroft AI