If you are running a unix system on a 32-bit Intel architecture machine, you should be able to use MIT Scheme. We distribute binaries for a few unix systems, but it is possible to compile MIT Scheme for other unix systems by following these directions. This can also be useful if you have one of the supported systems in a different configuration; for example if you use GNU/Linux but don't have X11 support installed.
tar xzf scheme-7.7.1-src-ucode.tar.gz cd scheme-7.7.1/src/microcode
./configure
make
cd ../../.. tar xzf scheme-7.7.1-ix86-gnu-linux.tar.gz cp -fp scheme-7.7.1/src/microcode/scheme bin/. cp -fp scheme-7.7.1/src/microcode/bchscheme bin/.