This package adds support for starting a guest session through gdm's flexiserver, which any already logged in user can launch.

it creates a temporary guest account with a temporary home directory and some restricted privileges (such as not being able to read any home directory or do any permanent change to the system).

call just guest-session to start the session.

the tutorial http://ubuntuforums.org/showthread.php?t=1566078 shows some ways to customize the appearance and behavior.