[father_of_two]

There is also scsh (scheme shell - http://scsh.net/) although not being maintained anymore.

[kd0amg]

There's a plan to do some work on it (including trying to port it to 64 bit) this summer.

[rml]

An updated version by Roderic Morris can be installed as a library atop the latest version of Scheme 48. It's on github: https://github.com/scheme/scsh

I think it's 64-bit (?). Most of the time it hasn't mattered for me, at least when writing scripts.

You can also just build the "old" version (0.6.7) with the `-m32` GCC flag, and it works fine on 64-bit Linux and OS X. It's very stable in my experience, and works fine.