Supported:

Dynamic typing.

Fully dynamic message dispatch with doesNotUnderstand: (called forwardInvocation:), proxies, Higher Order Messaging, etc.

Addition of (a) classes ( objc_registerClassPair() ) and (b) methods ( class_addMethod() ) at runtime.

Changing an object's class at runtime (objc_setClass() slightly hacky, but done by system services such as KVO, so supported).

Closures/Blocks.

Reflection.

Addition of (associated) instance variables at runtime. Interpreted languages can be fully interoperable peers.

Not supported:

Eval (but see above re: interpreted peers).

Continuations.

----

See: https://developer.apple.com/library/mac/documentation/Cocoa/...

EDIT: added references.