Rebol was closed source back when open source was really starting to take off with Perl and Linux. It is seriously cool (I agree), but the interpreter is a little slow.
Red still has a little ways to go, but could be a game changer some day. The project is insanely ambitious, but I'm optimistic.
The main (IMO sad) reason REBOL sits in a weird half-life position of "not quite dead, but..." is that, while REBOL Core is open, the GUI parts (which are crossplatform, and run on Linux) are still closed source.
It's a bit like .NET Core. Great to base a business on... not so great to tinker around with. Arguably the second (tinkering, learning) comes before the first (using what you've learned to build a business).
