My question about SOL got me thinking a bit.  It would be nice to have section in TUHS of any early clones that could be collected.   The two that I can think of that probably should be there are (other feel free to point ones that we should try to find):

1.) Idris, which was fairly true to V6 (enough that the one time I test it, things from pretty much just worked).  It was notable from being first.  Although the C compiler and the 'anat' (the assembler) were a tad different.  It the system that got Bill Plauger in trouble @ USENIX @ UDEL when he was booed for a 'marketing' talk.

2.) CRDS (pronounced Cruds by those of use that use it at the time) - Charles River Data Systems.   It was a UNIX-like system, although I do not think really attempted to hold to a V7 API much more than intent.  Although if my memory serves me, one of the unique features was the use of Reed & Kanodia synchronization in its kernel [REED79], which I was a always a fan.   The system was slow as sin bit it ran on a 68000.  [CRUDS system, a Fortune box and our Vax/750 running BSD4.1 were the systems Masscomp used to bootstrap].

Clem

[REED79] D.P. Reed and R.K. Kanodia, "Synchronization with Eventcounts and Sequencers"