scheme9 binary package in Ubuntu Focal amd64

 Scheme 9 from Empty Space is an interpreter for a broad subset of
 R4RS Scheme, and runs in many popular environments, including
 Linux, *BSD, the unmentionable horror, and Plan 9. The S9fES code
 strives to be simple and comprehensible. It is particularly
 interesting to people who want to (a) try Scheme without having to
 jump through too many hoops (S9fES is very portable); or (b) study
 the implementation of Scheme (in a language other than Scheme). A
 free online textbook describing the system is also available.

Source package