RONJA is optical point-to-point data link. Everyone can build one at home, because construction guide is freely available under GPL. Only things you need are some basic soldering skills and ability to drill and cut steel without crippling yourself :) .
The device have AUI interface and via PC based routers can readily interconnect two local area networks with speed of 10 Mbit Ethernet. Moreover communication is fullduplex.
Both sides of link consist of two optical heads, RX, TX and AUI interface modules. I have build one RONJA in 2003 to share computer resources with friends over housing estate.