Chez
https://cisco.github.io/ChezScheme/csug9.5/foreign.html#./foreign:h1
https://cisco.github.io/ChezScheme/csug9.5/io.html#./io:h16

Chibi
http://synthcode.com/scheme/chibi/lib/chibi/filesystem.html
http://synthcode.com/scheme/chibi/lib/chibi/pathname.html
http://synthcode.com/scheme/chibi/lib/chibi/process.html
http://synthcode.com/scheme/chibi/lib/chibi/stty.html
http://synthcode.com/scheme/chibi/lib/chibi/system.html

Chicken
https://wiki.call-cc.org/man/5/Module%20(chicken%20errno)
https://wiki.call-cc.org/man/5/Module%20(chicken%20file)
https://wiki.call-cc.org/man/5/Module%20(chicken%20file%20posix)
https://wiki.call-cc.org/man/5/Module%20(chicken%20pathname)
https://wiki.call-cc.org/man/5/Module%20(chicken%20platform)
https://wiki.call-cc.org/man/5/Module%20(chicken%20port)
https://wiki.call-cc.org/man/5/Module%20(chicken%20process)
https://wiki.call-cc.org/man/5/Module%20(chicken%20process%20signal)
https://wiki.call-cc.org/man/5/Module%20(chicken%20process-context)
https://wiki.call-cc.org/man/5/Module%20(chicken%20process-context%20posix)
https://wiki.call-cc.org/man/5/Module%20(chicken%20time)
https://wiki.call-cc.org/man/5/Module%20(chicken%20time%20posix)

Gambit
http://www.iro.umontreal.ca/~gambit/doc/gambit.html#Host-environment

Gauche
https://practical-scheme.net/gauche/man/gauche-refe/System-interface.html

Gerbil
https://cons.io/reference/os.html

Guile
https://www.gnu.org/software/guile/manual/guile.html#POSIX
https://www.gnu.org/software/guile/manual/guile.html#File-Tree-Walk

Kawa
https://www.gnu.org/software/kawa/Paths.html
https://www.gnu.org/software/kawa/Files.html
https://www.gnu.org/software/kawa/System-inquiry.html
https://www.gnu.org/software/kawa/Processes.html
https://www.gnu.org/software/kawa/Time-related-functions.html

MIT Scheme
https://www.gnu.org/software/mit-scheme/documentation/mit-scheme-ref/Operating_002dSystem-Interface.html