DoorKeeper allows you to set a message that will display before your visitor is allowed to enter your site. Draw attention to a new product or special offer; invite your visitor to take a survey; ask your visitor to accept or decline cookies. DoorKeeper is a self contained stack that will display the appropriate message and display two buttons e.g. 'accept'/'decline', 'take me to the homepage'/'take me to the special offer'. DoorKeeper then sets a cookie which will remember the users choice for a set period of time.

A useful stack, if you don't want to play with pop-ups, buttons and .js.

OnetimeRedirect will redirect your visitor to a landing page of your choice. Make your users aware of a special offer or a new product by taking them straight to a splash page when they visit your site. The result is more effective than a popup or a dedicated section on your homepage.
OnetimeRedirect can redirect your visitors to another page from any page it is placed on – It will only redirect once. A cookie will be set to prevent the redirection again until the cookie expires.

Bottom line: If you want to display a message before your visitor can enter your site, you now have two new stacks to choose from.