Wi-Fi Planet offers An Open Source Wi-Fi Roundup . Author Sean Michael Kerner states that:

Open Source is usually touted as a disruptive technology that is a boon to innovation and something that lowers costs and barriers to entry.

And the open source movement is having the same impact on Wi-Fi.

Here are a number of the project he describes:

• Linux LiveCD Router project. -- allows you to simply boot from the CD on an old PC with a Wi-FI card for a working Linux terminal, complete with a Wi-Fi Router.
  
• Sesame Wi-Fi
  
• Less Networks Hotspots Server (popularized by the Austin Wireless City Project in Texas).
  
• Public IP's ZoneCD is a simple Hotspot on a CD solution.