I've only used Tcl briefly, mostly for automation which it's great at. But it's a Algol-like imperative language, doesn't have any type of macros and makes everything based on strings (which makes sense for automation) instead of lists, with all the tradeoffs that comes with.
replyIt seems easier to figure out what the similarities are, because I think they're pretty few, they seem to differ more than they are similar.
Tcl being based on strings creates the same problems like in bash scripts, i.e. it is too easy to misuse the quotation rules, leading to subtle bugs.
replyUsing for scripting LISP-like languages is much more foolproof, especially for more complex scripts.
Ok, but now I want to embed Janet in a TCL program
replyJanet is faster, but lacks anything like tk. It's probably also quicker to learn, as you don't get into complex evaluation structure until you start messing around with quasiquotes, while tcl requires you to understand mixing 3 different layers of evaluation right off the bat. tcl's vm imo is easier to understand as well.
replytcl if you want a UI, janet if you want an embedded scripting language.