(borrowed from Wikipedia:)
PWB/UNIX (for Programmer's Workbench) was an early version of Unix, started in 1973 by Evan Ivie and Rudd Canaday to support a computer center for a 1000-employee Bell Labs division, which would be the largest Unix site for several years to come. PWB/UNIX was to provide tools for teams of programmers to manage their source code and collaborate on projects with other team members.
PWB/UNIX 1.0, released in July, 1977 was based on 6th Edition Unix. Notable "firsts" in PWB include SCCS, the remote job entry batch-submission system RJE, the PWB shell, written by John R. Mashey, which preceded the Bourne shell, lex and yacc, and utilities like find, cpio, expr, xargs, egrep and fgrep.
The files here come from spencer_pwb.tar.gz, donated by Henry Spencer.