I used to own a psion way back and also had a brush with the OS which morphed into Symbian on Nokia iirc. I loved the software architecture (which borrowed aspe

I used to own a psion way back and also had a brush with the OS which morphed into Symbian on Nokia iirc. I loved the software architecture (which borrowed aspects from the B5000), APIs and "services" and overall the focus on robustness. Some aspects like threads having their own heaps contributed to the robustness.