NPR (New Packet Radio) is a custom radio protocol, designed to transport bidirectional IP trafic over 430MHz radio links (ham radio). This protocol is optimized for “point to multipoint” topology, with the help of managed-TDMA. Bitrate is up to 500kbps (net, effective bitrate).

The radio modem is cheap (~$80) and home-made, with a 433MHz ISM module inside. The modem is connected locally with Ethernet, therefore no specific software is needed on PC.

Link

Update: here's another article that explains a bit of the history of the project.