Eiciel is a standalone tool and a Nautilus plugin to graphically edit Access Control Lists (ACL) of your files. ACLs allow to set more fine-grained permissions than the traditional Unix permissions of user, group, other (UGO permissions).
Eiciel also allows to edit the extended attributes of files and directories if the filesystem supports it.
Not all filesystems support ACLs and extended attributes. And even for those supporting them, they must be enabled (by the system administrator) before using Eiciel.