"ProxyHam" created controversy because the talk was supposedly suppressed by the US government. In this post, I'll describe how you can build your own, with off-the-shelf devices, without any code.
First, head on over to NewEgg. For a total of $290.96, buy two locoM9 repeaters (for $125.49 each), and two WiFi routers, like the TL-WR700N for $19.99 each.
Grab your first WiFi device. Configure it in "client" mode, connecting it to the "Starbucks" SSID. In this mode, you can then connect your laptop via Ethernet to this device, and you'll have access to the Internet via your WiFi device to Starbucks. In other words, it acts as a WiFi dongle, but one that you attach via Ethernet instead of USB.
Now grab your two locoM9 devices and configure them for "transparent bridging". In this mode, whatever Ethernet packets that are received on one end get sent over the air to the other end. Connect each localM9 via the TL-WR700N via the supplied Ethernet cable.
Now grab the second WiFi device and configure it as a normal WiFi router.
Now, assuming you aim the localM9's correct toward each other with reasonable line-of-sight, you've got a "ProxyHam".
The reason this works so easily is that everything has been designed to work this way. Bands like 900 MHz, 2.4 GHz, and 5 GHz are the "ISM bands" that are largely unregulated by the government. Unregulated means that if somebody is causing interference in those bands, you can't complain to the government to make them stop.
The 900 MHz band is attractive because the signal will go a lot further than 2.4 GHz. On the other hand, it's a smaller band, so can't carry the same speed as 2.4 GHz band or the 5 GHz band.
Industrial equipment use the 900 MHz band extensively. There are an enormous number of devices that'll bridge two wires in this band. Most of them are for simple serial protocols like RS232. Some are for Ethernet, like the locoM9. They tend be industrial grade things that cost a lot more. The locoM9 is the cheapest device that does this from Ubiquiti, but they have a lot of more expensive stuff to choose from, often with better directional antennas that'll go farther.
WiFi, too, is supposed to work this way. When you buy a WiFi router, you normally set it up in "access-point" mode. But virtually every router supports other modes, such as the "client" or "bridging" mode described above. It's supposed to work this way.
The point of "ProxyHam" isn't that there is some new magic out there, but that hackers can take existing stuff, for their expected purpose, but achieving an unexpected outcome.