If you see a road that you don't know where it goes RIDE IT and find out. If you don't enjoy it move on if you did enjoy it turn round and do it the other way
Agree with Tezza and JP there as there are some real delights found by just following your nose and see where you end up.
If you do feel the need for an app, then BBR or BestBikingRoads isn't too bad and free to use. Available for Android or Apple. Allows you to browse or create routes, including a "near me" option that looks for local rides. Contains routes from around the world too, if that appeals.
This alternative probably wouldn't suit Speed Jockeys but trying to follow a SatNav while riding briskly is looking for trouble anyway. It's not an app but I've had some memorable rides that I doubt I would ever have found, when using my Garmin Zumo sat-nav set to "Curvy Roads". Just set a destination and it'll do the rest.