I've been playing around with OpenWrt and Freifunk. There are special OpenWrt images for Freifunk. They are slightly modified vanilla OpenWrt images. They include for instance OpenVPN. The interesting approach here is that all traffic from the access point will be routed over the VPN, thus eliminating the liability for the provider of the access point: the traffic of the users on the Freifunk access point cannot (easily) be linked back to the ISP of the user. Especially in Germany this is important if you want to share your Internet connection.
The Freifunk images also support mesh networking, so it becomes possible to connect to Freifunk if your own router can connect to another Freifunk access point and relay the traffic. This way it is possible to make a mesh, and only one of the access points in the mesh needs to have an actual Internet connection that then can be shared. Brilliant!
I used the TP-Link TL-WR703N for Freifunk. It is not "officially" supported, but it was very easy to generate an image for it. It is a bit tricky to get working as there is only one ethernet port on the WR703N which is configured by default as the LAN port. It should be configured as the WAN port, perhaps I can modify the profile of the Freifunk firmware a bit to make it act as the WAN port by default.
This could also have a wider application, for example for eduroam. Together with eduVPN it makes for a compelling use case to use for instance the WR703N, available for less than $25 to promote eduroam everywhere from your home to libraries and cafes around the city. Minimal investment, great benefit for students and researchers!