Jonathan Gray wrote:
>> Any chance this DOS supdup software is still around?
>
> https://web.mit.edu/Saltzer/www/publications/pcip-1985.pdf
> http://www.bitsavers.org/bits/MIT/pc-ip/

Great, thanks!

It's a bit sad to read in supdup.mss "Unfortunately, very few machines
have TCP/Supdup servers.  The only servers known to us are on Mit-MC and
Su-AI, and 4.2 Unix machines running a server we distribute."  At this
point, three old ITS machines had recently fallen over, one after the
other, and MC was the only one left standing.  But not long after, four
new ones would appear.  One of which is still up and running!