Short bio: Computer Scientist, FOSS supporter (read more)
Tux Machines (TM)-specific
Ever since wireless Ethernet was born, a sizable number of folks decided that it should be freely available to the masses at no cost. So we have official community wireless projects, coffee shops, hotels, and other businesses supplying free wireless Internet, and a lot of purposefully-unsecured private wireless networks.
Humans being what they are, admins of open wireless networks should be canny and careful. In these modern times you can be punished for what other people do, no matter how tangential your connection to them. Presumably most folks would prefer not to go to jail because someone downloaded child porn over their wireless link, or spewed forth spams, or published information displeasing to corporate types. It's a good idea anyway to have some controls in place to control un-neighborly behavior, like bandwidth- and time-hogging.
Instant Wireless Communities
There are a number of specialized applications for building wireless portals.