[firlefans]

More interesting to my mind is this (Diamondback Ruby):

http://www.cs.umd.edu/projects/PL/druby/

Some features:

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Type inference:

DRuby uses inference to model most of Ruby’s idioms as precisely as possible without any need for programmer intervention.

Type annotations:

Methods may be given explicit type annotations with an easy to use syntax inspired by RDoc.

Dynamic checking:

When necessary, methods can be type checked at runtime, using contracts to isolate and properly blame any errant code, similar to gradual typing.

Metaprogramming support:

DRuby includes a combined static and dynamic analysis to precisely model dynamic meta-programming constructs, such as eval and method_missing.