Xfswitch-plugin is a user switching plugin for the Xfce4 Panel. It allows
you to leave the current session opened and open a new session with another
user. At the moment it relies on GDM, but other display managers will
be supported in the future.

Xfswitch is developped on git.xfce.org:
  git clone git://git.xfce.org/jeromeg/xfswitch-plugin