Guile is quite systems focused, as well, what with all the POSIX stuff it exposes. But neither Guile nor Gerbil can be used to implement their own runtimes. You

Guile is quite systems focused, as well, what with all the POSIX stuff it exposes. But neither Guile nor Gerbil can be used to implement their own runtimes. You need to write the GC, somehow. This is why Pre-Scheme exists.