checkgroup is a quick-n-dirty tool that parses the UNIX group file and outputs which groups each user belongs to. This was written because we had people in more than 16 groups and this chokes NIS ... so (radical idea! ;-), we wanted to keep an eye on this before it became an issue. You can sort the output by user or usage ... and optionally only show those folks who belong to more than ## groups.
It ALSO check the password file for any duplicate usernames and UIDs.
Finally, it flags any users listed in the group file that are NOT listed
in the password file.