There is nothing today that offers a similar level of accessible crossplatform development like Adobe Air. Qt is the only thing that comes close.
Sadly Adobe decided to kill the Flash platform. I wrote a long rant here a couple of years back: https://medium.com/@Pier/why-im-finally-breaking-up-with-fla...
Once Flex went to Apache and FlexDeveloper was killed, I just stopped paying attention.
There was a big stink around Jobs "Letters from Flash" and all AIR applications were put on indefinite hold in the app store review queue with no explanation. Adobe stopped development of their iOS stuff. Then after a few months all the apps were approved, Adobe resumed development, and no one had a problem since.
What is FlexDeveloper? Do you mean Flex Builder [now Flash Builder]? It wasn't really killed, just abandoned, if there is a difference.