Several GPS based Apps are available which some orienteering clubs set courses on. They are a way to set training without needing to put out control makers. They rely on mobile phone GPS signal which is OK in urban races and parks, but may struggle under tree cover.
Other useful Apps
What 3 words
This App divides the world into 3 x 3 metres squares and assigns three words as the unique identifiers to each square.
IOF list of orienteering software
This list includes the full range of software relevant to orienteering.