Force Login Popup Modal - WordPress

I’m looking for a popup login/registration plugin for the WordPress platform. I would like to be able to force visitors to login or register before they can use the site. These are examples:

http://www.zulily.com/ AND http://www.groopdealz.com/

You’ll notice that you can see the site faded in the background, but in order to use the site, the visitor must either login or create an account. I would like something exactly like this. I’ve seen a lot of plugins, but they don’t fade the background and/or they don’t offer the option to force login or registration. I would like something identical to those sites. Thanks!

Contact me form my profile page contact form, I can edit an exiting plugin for you to match your requirement of faded background with forced login.