As noted in “A Quarter Century of Unix”, Usenet played an important role for Unix users to exchange bug fixes and third-party source code, and just to communicate with each other. Here are links to some relevant newsgroups.

comp.sources.bugs: Bug fixes to systems and applications

comp.sources.games: Source code to games, some of which run on Unix

comp.sources.misc: Miscellaneous source code, some of which runs on Unix

comp.sources.reviewed: Peer reviewed source code, some of which runs on Unix

comp.sources.sun: Third-party source code for Sun systems

comp.sources.unix: Third-party source code for Unix systems

comp.sources.x: Source code related to the X Windowing System

net.v7bugs: Bug fixes for 7th Edition Unix

Here is a list of comp.unix newsgroups. The Internet Archive has a large collection of Usenet postings, but they are all zipped up.