I once used Tcl/Tk and am glad to see it’s still out there.
I’ve recently thought of using it again for fun.
I’m constantly amazed, but shouldn’t be, at how things like Tcl/Tk, that are used by various businesses to create applications, don’t take off into the mainstream.
I think about all of the effort today on the web using JavaScript. That’s using a language that could hardly do anything 25 years ago. But it wasn’t OS-specific, so it beat its competitor, VBScript, and later beat Applets and now Flash. I think the momentum that inspired V8 and development of great sandboxes, etc. was that JavaScript early on was fun for those that were creating their own webpages.
Tcl/Tk wasn’t fun, and neither were Java’s AWT nor Swing. So, maybe that’s why they didn’t stay around.
However, JS isn’t that fun for me either, these days. Constantly learning to do it “correctly” takes a lot of effort.
Personal opinion: Tcl was lots of fun and somewhat unique in being both a convenient scripting language and an easily embeddable language. But in the end Python and Lua became better replacements for those two specific areas (that's at least how it went in my case, I did lots of Tcl in the late 90's and early 2ks, but then switched to Python for "cross-platform-scripting").
There's still no proper replacement for Tk GUIs as far as I'm aware though, even Python uses it for building quick'n'dirty cross-platform UIs.
For simple scripting I've switched to Powershell (formerly Windows PowerShell). It's OSS, you can use it from the command line and it's available on Windows/OS X/Linux.