If we treat a blockchain like a gear, what solutions exist that can act as a gear train framework?

We talk about oracles but does such an oracle exist that can communicate or provide a message framework across multiple blockchains?

Looking for demonstratable examples.
I would think open transactions could fit this function, but I have not seen OT demonstrated like this action yet.

An alternative would be to write a messaging protocol that could be implemented across most standard blockchains... does this already exist?


Thanks for any insight on this.