What it is
Fabric OS is a browser-based desktop experiment. It boots into a taskbar-and-windows interface with a start menu, program manager, small programs and themes inspired by the desktop operating systems of the late 1990s and early 2000s.
What makes it interesting
The point is not nostalgia by itself. A desktop metaphor changes how a person explores a collection of tiny tools: programs become objects, state feels spatial and discovery is part of the interaction.
Why it belongs here
Fabric OS is delightfully hard to classify. That is a feature of fbc.ad, not a problem to solve.