[ih] What research capability-based OS was on the ARPAnet?

[John Gilmore]

When I was a teenager connecting to various computers on the ARPAnet via
the old Telenet/ARPAnet RS232 patch (about 1975), I used commands like
"@o 134" to open a connection to the MIT-AI computer, where I had a
tourist account and learned Emacs.  I used to try "@" other numbers, and
explore what else was out there; there were only a few hundred machines,
and most wouldn't let you get past a login prompt.

For a time, I ran across an interesting research machine that was based
on "capabilities".  It was well documented for its time, and I learned
about it by using it just to explore, but I never programmed for it.  By
now I've forgotten its name and who its inventor was.  Do any Internet
historians remember it?

	John
	
PS:  I may have been using an acoustic coupler at the time, in a
300 bps modem connection to a Telenet front-end.  Wow.  Things have
evolved since 1975.