Consider ZoneCD if You Have an Old PC Lying Around
If you have a spare computer, you can turn it into a hotspot gateway. ZoneCD is a Linux-based live CD that runs on generic computers and works with any wireless router or AP to provide public and private access.
Your Intel-compatible PC needs only 128 MB of RAM, a bootable CD-ROM drive, a floppy or USB drive, and two Ethernet network adapters.