Groups Permissions

Hi All,

   Is there any rails gem for maintaining groups and permissions. I am
really struggling on this for days. Please let me know if any. If
there is no gem to serve me I have to sit and work for the framework
component which can fit into any kind of application.

   My actual requirement is there are different users or the groups,
when they login we should show the same page with different content
and the links based on the user or the group. Expecting quick reply.

Thanks,
Ramu.