I have not tried it out but for iOS there's Side Pilot. It seems to be the only app for the Solo and I intend to try it. It is nowhere near as developed as Solex but the developer seems to be active with regular updates which is improving things on a weekly basis.
If you want to be a power user today it would seem you need to buy an Android phone.
I expect it has to do with @Kelly Schrock wanting to have a life rather than developing for two disparate platforms. Powerful custom or niche apps are non-trivial to maintain on two operating systems.
Though maybe if someone throws hardware and copious amounts of cash/beer at him he might acquiesce....
Or maybe not.....
Give SidePilot a go, I am updating it regularly, and other than Smart shots (it currently has its own versions of Follow, Orbit and Cable Cam which I will be working on making better over the coming weeks), it offers much more functionality than the stock app.