The long term goal of the Software Heritage initiative is to collect all publicly available software in source code form together with its development history, replicate it massively to ensure its preservation, and share it with everyone who needs it. The Software Heritage archive is growing over time as we crawl new source code from software projects and development forges.

Brief description of a failed attempt to install the virtual AGC
from https://www.ibiblio.org/apollo/ on a Raspberry π 4 running Raspian.

So you've written a UNIX utility, library, or driver—or have started writing one—and you want to document your work in a manual. What happens next?
Practical UNIX Manuals: mdoc is a guide for writing portable and maintainable UNIX manuals (manpages) in the mdoc language.
Why mdoc? Formatters for the language are available by default on all modern UNIX installations and may be downloaded for non-UNIX systems. Furthermore, mdoc annotates content semantically, not presentationally, producing consistent manpages across systems. For an analysis of mdoc and competing formats, refer to Fixing on a Standard Language for UNIX Manuals, published in the USENIX magazine.
I also feature the History of UNIX Manpages http://manpages.bsd.lv/history.html , which chronicles the development of manpages from the 1960s to the present day.

Overview of old unix versions which can be run on simulated (or real) pdp-11 computers.
The UNIX-HATERS Handbook, a review on https://athornton.dreamwidth.org/14272.html is also worth reading.

Guides how to install or run older UNIX versions in simh.
Also the UNIX Programmer's manual of V1-V6. V1-V6 are available as nroff output converted to html. V4-V6 are also available as troff'ed PDFs.
The site also has information about Plan 9 and pdp-6/pdp-10.

Blog about computer history, describing the source of cat(1), Lisp, RSS, Ada Lovelace's first program and more.

Dedicated to preserving the history and legacy of the
PDP-11 series of 16-bit minicomputers produced by
Digital Equipment Corporation from 1970 to 1990,
and by Mentec from 1994 onwards.

The project contains the VHDL code for a complete DEC PDP-11 system: a PDP-11/70 CPU with memory management unit, but without floating point unit, a complete set of mass storage peripherals (RK11/RK05, RL11/RL02, RK70/RP06, TM11/TU10) and a basic set of UNIBUS peripherals (DL11, LP11, PC11), and last but not least a cache and memory controllers for SRAM and PSRAM.

The design is FPGA proven, runs currently on Digilent Cmod A7 , Arty , Basys3 , Nexys4 DDR , Nexys4 , Nexys3 , Nexys2 and S3board boards. See section Complete Systems for more information.

5th Edition UNIX, 7th Edition UNIX, and 2.11BSD UNIX are known to boot, the hardware should also support DEC RT11 and RSX-11M, see section Running Systems for more information.

This is a retrocomputing project, rebuilding hardware from the late 70s and running historical software. To get into the tune see Figure D-1, a 11/70 console, and Figure F-2, a baseline system setup.

CPU History Museum for Intel CPUs, AMD Processor, Cyrix Microprocessors, Microcontrollers and more.
Also has information about processors used in space missions:
http://www.cpushack.com/space-craft-cpu.html

On-line collection of small computers from 1950-1990.