Information from Mike Speciner:
It was a timesharing system with a tree of processes for each user. PDP-11 memory management was used to isolate the users and their processes. The top-level process for each user was normally [PDP-11] DDT. There were software-generated interrupts of various sorts. A process could intercept the system calls of its children or let the OS handle the calls. We used this feature to write a process that emulated DEC's DOS so that we could use DEC's code to do things like run the assembler and compilers.
As I said, there was a DOS emulator. There was a version of TECO for use as a text editor. There was stand-alone SALV to clean up the disk. Disk blocks were pre-allocated so that a crash could make some free blocks seem like they were in use; SALV fixed that. But barring bugs or hardware failures, the disk data structures wouldn't get corrupted if SALV weren't run.
There were other user programs whose identity I no longer recall. And the server for the Camex product, a newspaper display-ad makeup system, ran under the OS on a PDP-11/35. The client was a less-capable PDP-11/05--using a different miniOS and running with an Adage display system. I seem to recall using DDCMP over some weird device to communicate between client and server.
There OS had drivers for various devices, including a software device for interprocess communication. The OS did not do swapping, so everything that ran simultaneously had to fit in memory. But multiple copies of programs shared their code spaces.
Information from Ed Schwalenberg:
Camex was a small Boston company that pioneered WYSIWYG terminals and typesetters for the newspaper industry (which at that time was one of the few industries that could afford $100,000 workstations). I worked there from 1978-87.
The first product, the Camex 135, was in use at the Boston Globe at the time I joined. It consisted of a PDP-11/35 running Camexec, a giant vector-stroke (not raster) CRT display run by an Adage image processor, and a large tablet that was the primary input device (paper menus on part of the tablet; the rest could be used to trace graphics, etc.). The end user never saw Camexec; it booted up automatically and ran the keyboard, tablet, image processor, 5-mb cartridge disk (used for the OS and application program storage) and 8" floppy disks (used to store the ads created on the workstation, one ad per floppy, no filesystem on the floppy).
Later products used Camexec on 11/34s to be a central storage system using CDC storage module drives (300 Mb each).
Camexec was written by Mike Speciner, who had been at the MIT AI Lab in the heydey of ITS and used ITS as his inspiration. There was also a DDT and a TECO as I recall.
Camexec was Camex-proprietary, and as far as I know was never used other than the embedding in Camex products. Dupont bought Camex in 1989, and pieces of it were later spun off to other newspaper-industry tech companies, so it's unclear to me who owns the IP at this point.