Currently we are in the midst of writing Angular v2 on top of the AtScript syntax. Here is an inventory of what is working today:
    - Traceur transpiler:
      - Consumes the AtScript syntax. (type annotations, meta-data annotations, fields)
      - Generates ES5 code with runtime type assertion statements for the rtts library and with meta-data annotations.
      - Transpiles AtScript into Dart code. (Does not do semantics matching, requires developer to use facades)
    - RTTS Library:
      - Asserts nominal types.
      - Asserts structural or custom types.
      -  Partial support for generics. Generics support in arrays and maps only.

If you look at this page here https://github.com/google/traceur-compiler/wiki/LanguageFeat...

You can see annotations in the "experimental" features list.