xindy, don't know if it is available on anything else than Linux yet. Thanks in large part to the heroic efforts of Vladimir Volovich, it is present for these platforms in TeX Live 2008: alpha-linux amd64-freebsd i386-freebsd i386-linux i386-openbsd i386-solaris powerpc-aix powerpc-linux sparc-linux sparc-solaris universal-darwin x86_64-linux karl