It seems like 90% of the uses for this can be taken care of with xargs:
echo "file1 file2" | xargs -P 2 gzip echo "file1 file2" | xargs -P 2 gzip echo "file1 file2" | xargs -P2 -n1 gzip
?And the version of xargs that is included with Solaris 10 doesn't have the -P option. In which case, installing gnu parallel is a slightly easier option than installing a different version of xargs.