Well, there were Momenta and PenPoint --- the latter in particular focused on Notebooks which felt quite different, and Apple's Newton was even more so.
Oberon looks/feels strikingly different (and is _tiny_) and can be easily tried out via quite low-level emulation (and just wants some drivers to be fully native say on a Raspberry Pi)
Oberon looks/feels strikingly different (and is _tiny_) and can be easily tried out via quite low-level emulation (and just wants some drivers to be fully native say on a Raspberry Pi)