Loginner gives you automatic access to other Wordpress backends you own, in one click.
Every account is put in the admin bar for easy switching.
Easy customization of active accounts and user rights.
WARNING: THIS PLUGIN CAN BE INSECURE IF NOT USED CAUTIOUSLY. USE IT AT YOUR RISK!
For more informations:
http://www.duckinformatica.it/prodotti-e-servizi/free-wordpress-plugins/
Best is to install directly from WordPress.
If manual installation is required, please make sure to put all of the plugin
files in a folder named loginner
(not two nested folders) in the plugin directory,
then activate the plugin through the Plugins
menu in WordPress.