Best implementations in 2025
These are all batteries-included with little care for standards:
- Racket
- Guile
- Gerbil
More exotic, modern lisps are also quite tempting:
https://ecraven.github.io/r7rs-benchmarks/
https://github.com/ar-nelson/schemepunk has r7rs libraries
On r7rs large or even r8rs
https://www.gnu.org/software/guile/manual/html_node/Guile-and-Scheme.html
With R6RS and R7RS, the unified Scheme standardization process appears to have more or less run its course.
for future directions, Guile takes inspiration from other related language communities: Racket, Clojure, Concurrent ML
we recommend using the parts of Guile that are useful in solving the problem at hand, regardless of whether they proceed from a standard or whether they are Guile-specific.
From #scheme:
03:31:24 PM - wingo: guile’s r7rs implementation should be fine. it is not a main focus however. most people that write scheme programs tend to target one implementation. targetting a standard is possible but not the easiest thing to do 03:32:04 PM - wingo: my pov is http://wingolog.org/archives/2013/01/07/an-opinionated-guide-to-scheme-implementations, see the “you and your scheme” section