REBOL is the "Relative Expression-Based Object Language", created in 1997 by Carl Sassenrath, also known for AmigaOS. It has been described as a "dialect-oriented", having a very similar syntax to Tcl and (in Carl's words) "its greatest strength is the ability to easily create domain-specific languages or dialects". Ward's wiki has some examples .
Rebol was open-sourced in 2012, leading to some resurgence in its popularity. The ren-c project is aggressively overhauling the implementation to push open-source development on REBOL and Red further.
Historically, REBOL was very much a scripting language rather than for "serious application development" (no threads, rasks or event loop), though as of 2015 a lot of ground has been gained. Tcl'ers may have qualms about the many, many first class types in REBOL (email addresses have a type!), but will find much its the "dialect-oriented" nature and clean syntax comfortingly familiar.
What: REBOL to Tcl interface Where: From the contact Description: Contact posted a small example to comp.lang.tcl, demonstrating how simple it was to set up a client server between REBOL and Tcl/Tk interpreters so that REBOL could do graphics in that fashion. Intended only as a proof-of-concept demonstration. Updated: 07/1999 Contact: mailto:[email protected]
RS likes the very minimal assignment syntax in REBOL:
which a radical language modification gives you in Tcl too...
Another Scripting Language.