The app lets you get the arrival times for buses, trams and trolleys. You can get all the stops on a certain line. Stops can be saved in favourites. The map can be used to show the stops in the vicinity of a location or the location of a favourite stop.
The times shown in the app are extracted from the SUMC website(the virtual tables), which means they are based on the GPS coordinates of the bus/tram/trolley, and are as accurate as possible.
Time extraction from the SUMC website is thanks to Ivaylo Stoyanov(https://github.com/ivkos)