RONJA (Reasonable Optical Near Joint Access) is a Free Space Optics device originating in the Czech Republic. It transmits data wirelessly using beams of light. Ronja can be used to replace a segment of LAN, and one can enjoy all activities as if they were directly connected via 10Mbit/s full duplex Ethernet ” playing games, connecting to the Internet, streaming audio/video, or sharing files.

The range of the basic configuration is 1.4 km (0.9 miles). The device consists of a receiver and transmitter pipe (optical head) mounted on a sturdy adjustable holder. Two coaxial cables, like those used for TV antennas, are used to connect the rooftop installation with a protocol translator installed in the house near a computer or switch. The range can be extended to 1.9 km (1.2 miles) by doubling or tripling the transmitter pipe.

Building instructions, blueprints, and schematics are published under the GNU Free Documentation Licence. Only free software tools are used in the development. The author calls this level of freedom "User Controlled Technology". Ronja is a project of Twibright Labs.