APRS, or Automatic Packet Reporting System, has been popular on the Amateur Radio packet band for over 20 years. It is the brainchild of Bob Bruninga, WB4APR. While many are familiar with its vehicle tracking capabilities, it is really much more. It is recommended that you have a look at Bob's own site and other information about APRS.
APRS can be used as a SMS (Small Message System) app to send messages or bulletins to other APRS users. It has the capability of sending emails, as well. It can also be used to highlight special events, like Ham-Ex, on a map. And of course, it does allow APRS equipped stations to be tracked in real time on a map. This includes vehicles, bicycles, walkers/runners, aircraft, balloons, etc.
There is a common frequency used across North America for APRS: 144.390 MHz. Users can receive APRS data via their 2 meter radios and using APRS software, view maps, read messages, etc.
There are also web-sites that are updated automatically from IGate stations around the world. An example of this is aprs.fi.