Regular lobste.rs readers may already be aware of this, but if you’re interested in Rebol you ought to give the Red programming language a look. It’s a modern language strongly based on Rebol.
If you don’t mind I’ve got some questions:
I wouldn’t say that Red is production-ready, but development is moving quickly and their dev blog is an interesting read.
Red and Rebol overlap significantly, but neither is a perfect subset/superset of the other.
Red is doing some interesting things with their implementation. The language is split into two parts: a high level part and a C-like part. The whole language is self-implemented, and it’s easy to cross-compile executables.