This list is dedicated to nonelectronic nautical navigation. Its members share a common interest in this art, finding great joy in using dead reckoning, compasses, parallel rules, and sextants to plot exact positions on the ocean. The second example is the BSDI users list. This list discusses anything associated with the BSDI UNIX operating system. Members on this list include owners of the BSDI operating system, both expert and novice.
Discussion spans the gamut, from how to install an update to how to configure a mailing list.
The last list is Navision Users Group. Questions here range from how to program the system to how to correctly set up the inventory system for a particular company. These lists represent a wide range of interests and hobbies. Membership put me into several different communities all at the same time. There are other examples of mailing lists' becoming more formalized by moving from a collection of individuals without a formal organization to becoming structured associations.