I haven't done much with ham radio in awhile, but I recently learned a little about APRS. It stands for Automatic Packet Reporting System and it is really interesting.
I currently only have a few Baofeng UV5 $25 portable radios, so I have downloaded APRSdriod on my phone to play around with the system. Basically, the system allows real-time tactical digital communications of information of immediate value to the local area. It can be use for messages, alerts, announcements and bulletins, etc.
You can track users and stations on a map, which allows you to see their call sign, GPS location and any information relating to frequencies they are monitoring or the equipment used to provide the location, such as TinyTrak devices.
One of the sites you can use to check activity in your area is aprs.fi just plug in your zip code in the right column.
There is still a lot to learn about aprs, but I am enjoying the learning process.