A quote from the Guile tutorial at [L3 ]: "One of the things that Scheme as a programming language is particularly good at is the emulation of other programming languages. This means that your users don't actually have to write their extension scripts in Scheme; instead, they can write the scripts in Tcl or Python, and just load up the appropriate chunk of Scheme code to emulate that language. (Or at least they will be able to, when the appropriate translators have been written.)"
freshmeat lists 43 projects that mention Guile and 430 for tcl.
"There's some humor in the idea that Guile started out with the stated goal of being a Tcl killer. Years later, a Guile install is almost 8 times the size of a Tcl install and it introduces significant external dependencies. The licensing is also worse for inclusion in larger systems." [L5 ]