Usenet began in the 1980s as a collection of discussion groups, mostly for college students and staff on any topic the users decided they wanted to talk about. Anything without limitations. Whenever a quorum decided a new topic was needed, it was added.
A company called DejaNews began organizing the Usenet archives in the late 1990s, and Google bought them in 2001 and formed Google Groups. Google Groups serves as both an archive going back to 1981 and a continuation of all the discussion groups. (This has frightened many former college students who began to ask, "Everything I posted there is now available for potential employers - or my kids! - to read? Forever?" Google used to provide a method of claiming old posts and deleting them, but that help page is no longer there, and they only explain how to delete more recent posts to Google Groups.)
A few of the groups that might be of of obvious interest to genealogists and family historians: Alt.Obituaries, and two dozen groups or so under the heading Soc.Genealogy.
Of course you can search all groups at once on the main page, including newer ones created under the auspices of Google Groups. Just be forewarned. In the search results, before clicking on something, take a look at what the title of the discussion-group is. This will likely give you a clue as to what posts you are likely to find in that group. This could change your mind on whether or not to read the post.
This post was adapted from a post back in August of 2007.