What is old is new again: linking open source Unix-alikes, native cluster OSes for massively parallel computers, and 1980s platform rivalries. You get all this in a somewhat dusty project hoping to "breathe new life" into Helios, a manycore OS from the '90s.
Back in the 1980s, Intel couldn't build you a box with that many cores – but a small British outfit called Inmos could. While a remote descendant of Inmos provides one of the processors in relatively recent Amiga hardware, there's a much older connection.
There were three home computers that teenage British proto-geeks could aspire to owning: Commodore's Amiga, Atari's ST, or the British alternative, Acorn's Archimedes. While the ST had an off-the-shelf OS using Digital Research GEM, both Commodore and Acorn tried to build all-new OSes, and when those efforts failed, resorted to adapting pre-existing code. Acorn Arthur, later renamed RISC OS, drew heavily on the BBC Micro's OS, MOS.
King and some other team members subsequently left and started a new company, Perihelion Software, which created a new OS, Helios, for the Inmos Transputer. At least somewhat Unix-like, Helios was intended for many-processor parallel computers, and extended TRIPOS's lightweight message-passing architecture to coordinate processes running on separate CPUs.
So when Atari launched its Transputer Workstation, the ATW800 or ABAQ, it ran Helios. Ironically, given that MetaComCo originally pitched the idea at Commodore, when a household name launched a Helios machine, it was Atari hardware – running a distant relative of AmigaDOS.
Helios didn't die with the Transputer. It was later ported to other CPU architectures, including Arm – it was the basis of Acorn co-founder Hermann Hauser's early pen-driven computer, the Active Book. (We recommend the promotional video.)
There's quite a lot of documentation, source code, and even installation media available, both for the original version and later editions. Perihelion's introductory book, The Helios Parallel Operating System [PDF], begins gently and readably, and the first chapter or two form a good starting point.