From the Guile web page:

Guile is an interpreter for the Scheme programming language, with support for many SRFIs, packaged as a library which can be incorporated into your programs. Your users have full access to the interpreter, so Guile itself can be extended, based on the needs of the user. The result is a scripting language tailored to your application.

To reproduce my results on Ubuntu Gutsy Gibbon, install Guile with

sudo apt-get install guile-1.8

and create a file containing

(use-syntax (ice-9 syncase)) (read-enable 'case-insensitive)

named, say, `guile-load-options.scm`

. Then run the
interpreter with

guile -l guile-load-options.scm 2>&1

Guile makes the following choices:

- Complies with the R5RS letrec specification even if the expressions being bound return more than once (via capturing and reentering their continuations). (more)
- Evaluates unquoted vectors to themselves. (more)
- Allows the '*' procedure to return exact zero when a factor is an exact zero, even if other factors are inexact. (more)
- Allows division by inexact zero. (more)
- Supports arbitrary precision literal integers. (more)
- Supports arbitrary precision computed integers. (more)
- Supports the literal syntax for rational numbers (e.g. 1/2 is the literal number one half). (more)
- Supports the literal syntax for complex numbers (e.g. 1+i is the complex number with real and imaginary parts both 1). (more)
- Supports nontrivial exact rational numbers (e.g. (/ 1 3) produces an exact one third, not a floating point approximation). (more)
- Guesses the denominators of inexact numbers per R5RS. (more)
- Propagates division by zero errors from 'string->number' (more)
- Requires the 'remainder' function, and related ones, to operate only on integers, a la SRFI-94. (more)
- Does not define the procedure 'transcript-on'. (more)
- Does not define the procedure 'transcript-off'. (more)