I strongly recommend Haxe + OpenFL. Haxe is a language based on ActionScript. There are a few differences but its the closest to what you know. The language manual and API reference at http://haxe.org are great resources.
OpenFL is the Haxe implementation of the Flash API, you can find info on OpenFL at http://openfl.org (this is the best place to start, make sure to check out the API reference). OpenFL doesn't implement the entire flash API but it should suffice for most of your needs. You should also check out OpenFL's feature matrix at http://www.openfl.org/documentation/technical-overview/feature-matrix/ to see what's supported or not.
Lastly you'll need Lime...this is the program that compiles Haxe to various targets including PC, MAC, HTML5, iOS and Android (and even some game consoles). Lime is a command-line tool but its fairly easy to pick up. OpenFL.org has installation instructions for the entire suite of tools. You can get started at the following link http://www.openfl.org/documentation/getting-started/installing-openfl/
If you need to ask further questions about OpenFL make sure to join the community forums at openfl.org.