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Twitter post by Daniel Feldman (@d_feldman): Linux is the only major operating system to support diagonal mode (credit [Twitter] @xssfox). Image shows an untrawide monitor rotated about 45 degrees, with a horizontal IDE window taking up a bottom triangle. A web browser and settings menu above it are organized creating a window shape almost like a stepped pyramid.
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Smart watches tend to be microcontroller class devices because even though you can fit something powerful in there, powering it and heat dissipation make it silly.
The usual embedded-type application for wayland that it's even especially designed for is automotive: Things without window management but not particularly hardware-restrained. Also think public transit ticket machines, ATMs, such things. In that sense, from wayland's perspective android is already desktop.