AIS stands for "Automatic Identification System". It's an automatic tracking system used on ships and by vessel traffic services. AIS information supplements marine radar, which continues to be the primary method of collision avoidance for water transport (definition sourced from Wikipedia).
There is a lot of traffic at sea, especially near certain coasts, making it necessary to be seen by other means. We have radar, but it uses more power than AIS to function. With radar we can know that something is out there, but we don't know the boat's name, size or heading. AIS provides all of this information, with it, you can call a boat by name on the radio if need be, and they, can see you and call you as well if you have a transponder (a device that transmits your boat's information).
Aboard pino we have a Vesper XB-8000 transponder.
It is possible to route the AIS information to a chart plotter. We connect to our unit's WiFi signal and can look up targets via an app called Watchmate. The app works well, it is easy to add and remove proximity alarms. When in a busy harbor, with more traffic, our alarm configuration is different than at sea. Overall, we would prefer not to rely on an app for AIS, because apps drop in an out of existence, but for now it's what we use and it seems to work fine. Even without an app, AIS would warn of of ships, and broadcast our position, which is really what matters.
See our ais installation.