We’ve already written about the excellent Radio Garden service, which lets you listen to radio from all over the world. But while Radio Garden is essentially a directory of official radio station streams, WebSDR is about something else entirely: it aggregates addresses of servers connected to SDR (software-defined radio) boards—hardware capable of capturing an entire frequency band (or even several at once). You can read more about them in Hacker issue 177.
Once you pick one of the user stations, you can tune the receiver yourself and hunt for something interesting. There are plenty of tools for tuning and signal visualization (available in HTML5 and as a Java applet). There’s even a chat where you can talk with other listeners and share your finds.
The creator says he first launched it to share a live stream from the Dwingeloo Radio Observatory between universities. Later, it turned out others wanted to run their own WebSDR servers to stream captured radio signals to the internet. You can request the server software from the owner of WebSDR.org by emailing him. Anyone who sets it up is automatically added to the site’s directory.