Does Haiku/BeOS have a lineage, were they built off of some other OS in anyway or just their own thing which took what it liked from what was already around and started from the ground up?
At the time, Be often talked about it being clean, legacy-free, ground-up etc.
The main _inspiration_ was the Amiga, but not really AmigaOS.
BeOS was built in the still-new C++ but AIUI predates a lot of standardisation of C++ which subsequently happened -- as was Psion's EPOC32 and its later rebranding as Symbian.