FabFi is an open source project that is linked up closely with MIT’s Fab Lab and the university’s Center for Bits and Atoms and has been up and running in three sites in Kenya and Jalalabad. How it works is that it uses readily available commercial wireless routers which are then mounted on homemade RF reflectors covered with a metallic mesh surface. Another router-on-a-reflector is set up at a distance and the two routers then create an ad-hoc network that provides internet access to a whole network of reflectors. The number of reflectors which can be integrated into the network is theoretically endless, limited only to their supplies, and as of now FabFi’s network covers most of Jalalabad.
The devices are run off an automobile battery which also means that they will be able to pack up their equipment and set up in another location if necessary. It’s low tech, but it works. For more information about FabFi (and even how to build your own) just head on down to their WikiHome page.