FW: If you like Tcl for its high-level programming style, simplicity and cross-platform compatibility, you may also want to check out REBOL, or its much younger descendent, Red.

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.

• an ONLAMP article from 2003 about REBOL and its VID graphical extension.
• Dr Dobbs in 2000 and a related HN discussion from 2015

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http://www.rebol.com/

 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:icimjs@loop.com

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RS likes the very minimal assignment syntax in REBOL:

 var: value

which a radical language modification gives you in Tcl too...

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Another Scripting Language.

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