Multi part answer:
1) There are a number of generic Android apps that can act as clients for a tracking system and also provide a map based interface to view the locations.
for example: Real Time GPS Tracker GPS Tracking Pro
Also have a look at http://www.heavy.com/tech/2013/07/top-best-gps-apps-for-android-2013/
2) There are also GPS tracking apps for Android that allow you to specify your own server as the recipient of tracking data.
3) The most often used API for display of tracking data is the google maps API Version 3
The advantage of developing your own viewing software is that you completely control the look and feel, the performance, and to a great extent the availability and reliability.
Development of apps using the Google Maps API is not extremely difficult once you understand the 'culture' of the API. There is extensive help and support available online.
Probably need more detail about what you're trying to accomplish to provide more info.