I think the question is what does portable mean, or is there a better word to use than portable. It clearly doesn't just mean written in C or C++. From the linked page -- "It currently runs under CLisp and SBCL, Clojure, Scheme, Ruby, Python, the JVM and Javascript."
In the sense that they run under CLisp, SBCL, Clojure, Scheme, Ruby, Python, the JVM and Javascript? I can't think of any that are portable in that sense.
Definitely seems to be -- they claim it's been used by a lot of different people (including, notably, the now-famous indie game Papers, Please) and is somewhere deep into version 3.something -- it's been around for quite some time.
From[0], the answer appears to be yes, but it greatly depends on the host. One can write Common Lisp code by using uppercase. Using $native will execute the following code as Scheme code. For Clojure, it looks like Shen provides a FFI for basic interactions.
