Andor's Trail
Andor's Trail is a free and open (FOSS) single player RPG for Android. Although still under heavy development, the game is already fully playable, and the world map, quests and story is very impressive, with more to come.
Recently, an updated beta version was released, with even more maps and quests. The game is available from the FOSS market f-droid.org, and Google's Play Market.