My code uses the following language features; for each, some systems lack some features.

1 (let* ((a 2)(A (- a))) a) => 2 ; case sensitive!
2 call/cc ; the name, (not the function) is convenient
3 (if #t 7) ; (sort of important) 
4 (λ () 3) ; convenient
5 scheme-report-environment; vital
6 (define ((add a) b) (+ a b)) ; convenient way to define a curried add.
7 (expt 2 100) ; bignums are needed when they are needed.

1, 2, 4 & 6 are not required by R5RS.
7 is standardized but not required by R5RS.
I use 2, 4, 5, 6 & 7 only intermittently.

Which systems have which features:

352 [1 2 3 4 5 6]
mzscheme 372 [1 2 3 4 5 6 7]
http://download.plt-scheme.org/bundles/4.2.5/mz/mz-4.2.5-bin-i386-osx-mac.dmg
  MzScheme v4.2.5/bin/mzscheme [1 2 4 6 7]
  MzScheme v4.2.5/bin/plt-r5rs [3 5 6 7]
  MzScheme v4.2.5/bin/swindle [1 2 3 4 7(?)]
kawa 1.9.90 [1 2 3 5 7]
N.B. PLT 352 & 372 yield 1/2+1/2i for (/ 1+i).

PLT Scheme

Just now (2011 Mar 28) I find MzScheme 372 performes all of the code here that I have tested. The 4.2.5. version provides some language alternatives but each alternative lacks some vital feature. The language reference
This page bears on the problems and perhaps the solution. (too)

I run MzScheme 372 as follows:

I launch (double click) the file “plt-372-bin-i386-osx-mac.dmg” which causes a ‘virtual disk’ to be mounted and appear on the desk top.
Launching “PLT Scheme v372/bin/mzscheme” on that disk creates a Terminal window running a REPL.

By typing “./plt-r6rs ~/test” in a shell in /Volumes/MzScheme v4.2.5/MzScheme v4.2.5/bin , the program executes the file “~/test” which reads:

(import (rnrs))
(display 42)
(newline)

and sure enough 42 appears as terminal output. This is a poor interactive environment! The environment there does not define the symbol read-case-sensitive.

There are several terms used technically whose definitions I have not found such as ‘namespace’. They are used in explaining the logic of the system.

Kawa

I fetched kawa which produces a directory. With a shell in that directory I typed:

./configure
make
java kawa.repl

I got a REPL program that failed only feature 4. I have xcode installed on my Mac. I tested most of the repository test cases and they all passed.