I'm ReViewer's author and ReViewer is 100% REBOL made ( http://www.digitalbums.net ).
I chose REBOL because it is very lightweight and it is an homogeneous solution.
Does anybody knows a cross-plateforme language with internal GUI capability?
I know SDL, which is nice, but it is C library, less productive than REBOL is.
I know the QT library... and they say that what they do is a revolution. But it is not free and it works "only" on Win, MACOSX and Linux when REBOL/View runs on more!
Finally, I know many heterogeneous solutions like Python + TK, Python + SDL, Ruby + ... Following that way is possible, but I don't like much! and I'm not sure to find a true cross-plateforme set without having to write any specific plateforme code at all!
It is absolutely the same with network!
Now, take both the GUI and networking and you got an X-Internet browser! Running on many OS!!
If we forgot GUI, REBOL/Core is Free for all uses (personal, commercial, educational), so?
REBOL itself is a productive and elegant programming language and the only thing I which is a long life to REBOL!
Fianlly, a GPL project named r-sharp is on the way on sourceforge. It is a REBOL clone, still alpha state, but...
Considering REBOL only from a licensing point of view is a little bit blind!