Thoth has been a white whale for me for decades.
Ditto. Although, I believe the late John Beety had his 'Thoth Thucks" tee shirt for years. I believe Kelly Booth still does.
AFAIK nothing has survived from it.
You can argue that V-Kernel and QNX are children of Thoth - but they were both in a flavor of Waterloo C that did not think ever targeted the PDP-11 [that might be a misunderstanding WRT Waterloo C].
"Decus" (Conroy's) C (transliteration of the assembler Unix C) should also be mentioned.
Hmmmm, it's a flavor of Dennis' compiler in disguise and was sort of an end-around for the AT&T lawyers by taking the *.s files, and converting them to MACRO11, and then
redoing the assembler code to use originally RT11 I/O and later RSX11. That said, it had its own life and ran on the DEC OSses, not UNIX, so it probably counts.
That said, I thought Paul was asking about different core compiler implementations, and I would argue the DECUS/Conroy compiler is the DMR compiler, while the list I offered was all different core implementations.
I'm curious about Jon and Tom's MOD2 compiler. Other than Wirth's, which targeted the 68000, Lilith, and VAX, I did not know of another for the PDP-11. Any idea of its origin story? I would have expected it to have derived from Wirth's Modula subsystem. FWIW: The DEC Mod-II and Mod-III were new implementations from DEC WRL or SRC (I forget). They targeted Alpha and I, maybe Vax. I'd have to ask someone like Larry Stewart or Jeff Mogul who might know/remember, but I thought that the font end to the DEC MOD2 compiler might have been partly based on Wirths but rewritten and by the time of the MOD3 FE was a new one originally written using the previous MOD2 compiler -- but I don't remember that detail.