It's still great at what it was always great at: embedding, acting as a CLI, and doing random grunt work. It's Lua's main competitor, but it can also go toe-to-toe with python and ruby in terms of libraries in some areas (although by no means all of them). In particular, the ease of construction for graphical applications is arguably unmatched (IUP is probably the closest), SQLite was built to work with it, metakit is handy as well in the DB area, it has a great event loop, several OO models, solid unix integration, sold FFI and excellent embedding (as you'd expect), Starkits, which means you can distribute your whole TCL sourcetree as a single file, and a ton of other stuff.

So while it's not as popular, relevancy isn't an issue.

Hah yeah I realized that meta joke after I posted

Can I get your email? Would love to hear about that stack