Mark Williams Company sources

Coherent is now free software. The source tree is a bit of a mess -- but it has version control information back to 1990 for much of the code, so it'd be eminently suitable for a reconstruction project at some point. (However, I don't think there'd be much point in trying to resurrect the utilities for modern use; they're full of arbitrary limits...)

to coherent retrocomputing software source unix xybasic ... on 17 March 2015

The EdgeBSD Project: About EdgeBSD

Another NetBSD branch, using Git as the VCS. (It's not clear to me what the "desktop based on DeforaOS" thing is about...)

to bsd git netbsd operating-systems unix ... on 17 March 2015

LSX Unix Restoration page

"For a very long time, the smallest Unix system for the PDP-11 compatible machines - LSX, adapted from Unix V6 by Dr. Heinz Lycklama - was feared lost because it was never officially released outside of Bell Labs and nobody bothered to keep it for posterity." Now they have.

to history lsx os pdp11 retrocomputing unix ... on 05 March 2015

FreeMiNT - SpareMiNT Wiki

"FreeMiNT is a free, open-source operating system for 16/32bit Atari computers and clones, based on the original MiNT by Eric Smith and officially adopted by Atari Corp. It is compatible with TOS, but adds a lot of new functionality not available in any other TOS-compatible operating system."

to atari mint os retrocomputing software tos unix ... on 20 January 2015

dspinellis/unix-history-repo

A merged Git repo containing the source history of Unix from the earliest C versions up to present-day BSD. Very neat!

to bsd git history retrocomputing unix ... on 18 January 2015

EtchedPixels/FUZIX

Alan Cox's extended version of UZI, a SysV-ish Unix for 8-bit microprocessors. (I'm trying to persuade myself that it doesn't need a BBC Micro port...)

to 6502 6809 os retrocomputing software unix uzi z80 ... on 16 November 2014

Time, Clock, and Calendar Programming In C

Nice explanation of the various historical stages of development of the C time APIs.

to ag0803 api c calendar date posix time timing unix ... on 03 October 2014

xiaq/elvish ยท GitHub

A pretty fancy shell written in Go.

to go shell software unix ... on 24 August 2014

Xv6, a simple Unix-like teaching operating system

The teaching OS for MIT's operating systems course -- which is taught by Russ Cox, Frans Kaashoek and Robert Morris, so it's probably safe to say that the authors know what they're talking about! This is a cleaned-up Unix v6 -- contrast with v7x86, which is a modernised Unix v7.

to os software teaching unix xv6 ... on 27 April 2014

LITCAVE

Replacing a Unix userspace more-or-less from scratch, including a compiler, libc, and so on.

to c compiler minimal software unix ... on 22 February 2014