[umanwizard]

What, for example? The only other one I can think of is Lua and IMO it’s quite debatable whether that is more established than Guile.

[tomn]

please compare:

https://archlinux.org/packages/extra/x86_64/lua/#pkgreqs

https://archlinux.org/packages/core/x86_64/guile/#pkgreqs

(lua at least is under-counted as there is luajit, lua51, and various packages which embed their own version, e.g. pandoc)

[cmm]

It is at least used outside of the GNU Project...