This app was mentioned in 3 comments, with an average of 1.33 upvotes
https://play.google.com/store/apps/details?id=com.rpgautomails.fatedice
2 years old. Simple dice roller. Looks nice
https://play.google.com/store/apps/details?id=com.hiddenachievement.DeckOfFate
Recent and official. Mostly just a pretty dice roller. Not free
https://play.google.com/store/apps/details?id=com.pingdevelopment.gmtoolkit
Campaign tracker with Fate Core sheet support.
FAE character sheet tracker and dice roller. Last updated in February
That Atma RPG looks neat and appears to be well suited to what you are looking for; what about Atma is making you look for alternatives?
As for a simple RPG requiring little preparation, you can get a new game of <em>Fate Accelerated</em> up and running in mere minutes by initially defining only a character's Concept, primary Aspect, highest Approach, and Trouble, and deciding the rest during gameplay. You can use an app for Fate dice rolls. *Fate Accelerate*d is also on Roll20.net.