Google is a search engine for human readable content. Shodan does the same for machine readable content.
You can:
- search for specific IP addresses, and it will show you the active ports, and running services.
- search for a specific response header in the set of countries
- browse through the screenshots of open VNC & RDP
- open webcams
- and more...
The free accounts can use any feature, but the list of results is limited. But if you really want to look under the deck of the internet, the subscription is worth it.
I was running tvheadend with dvb-t usb stick at the time, and one day wondered, who else might be running it. There were quite a few all over the world.