Criss Swaim

When this plugin is active and the option enabled, it checks for a logged in user. If the visitor is not logged in, then the user is redirected to another site as defined in the redirect path option or will display a page with message as entered on from the settings. If logged in, site acts as normal.
Sites with this plugin active must access the site with sitename/wp-admin and log in.
<h3>Usage</h3>
Install the plugin 
Go to the settings page 
Set the address for the redirect
The active/inactive switch allows temporary disabling of the plugin

TPG Redirect

if a user is not logged in, redirect to site specified site or show page with user defined message.

swartwerk

This plugin displays a blank page for all unauthenticated visitors. Any user logged in, with any capabilities, can see the site.

Blank Page

This plugin displays a blank page for all unauthenticated visitors. Any user logged in, with any capabilities, can see the site.

TPG Redirect vs Blank Page