TACMAP tactical map application let's you add and edit tactical map markers on a map, Finnish maps include terrain, basic and aerial views from Maanmittauslaitos. OpenStreetMap and satellite -maps covers the entire world. You can also see your GPS location in real time on the map.
You can also share your tactical map markers and location with other users by accepting a user invitation to follow you. You can also see other users map markers and locations on the map if you allow them.
To use markers and location share, you need to sign up for the service (http://tacmap.maanpuolustus.net/). Tactical markers are MIL-STD-2525C / NATO APP6B standard.