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.

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.

Blank Page vs TPG Redirect