Recs.
Updated
Haxe is an open source toolkit based on a modern, high level, strictly typed programming language, a cross-compiler, a complete cross-platform standard library and ways to access each platform's native capabilities
SpecsUpdate
Pros
Pro Syntactic macros
Syntactic macros allow you to extend compiler features at the syntax tree step. Macros come into play after code is parsed into the abstract syntax tree, and macros allow you to transform it before the rest of the compilation completes.
This provides for immense power, while at the same time scoping the extensibility at a level that is powerful, but well constrained.
Cons
Con Lack of learning resources
Haxe is only for people who already know ActionScript and have followed the project from the beginning. All the textbooks are out of date, as is the official documentation. There's no way to bring in new team members.
Nov./2018 : This must be a very outdated CON, notable efforts have been made to make it more accessible. Some level of programming know-how is required to enter Haxe development, such is true.