I commented elsewhere that the source code of First Edition Unix had been restored from tapes. The response was amazement and a request for more information.
What have people done? Who did it? When? And how?
In 2008–2009 The Unix Heritage Society managed to reconstruct the source for First Edition Unix kernel and parts of the shell from various sources, including magnetic tapes and paper documents. The details were written up and presented at a USENIX conference in 2009.
There have been other papers.
Originally, the source was available on Google Code. Google Code of course proceeded to then turn up its toes and die, and all that is left there is a badly-marked up archive.
First Edition manuals available in digital form had also been made available.
In more recent work, Diomidis D. Spinellis of the Athens University of Economics and Business has integrated this and others into a reconstructed combined GitHub repository encompassing some 40 years of development, from First Edition here and other Research Unix versions through 386BSD to FreeBSD 11.0.