Anthony

This plugin will limit access to the site. Only visitors with a cookie token will be able to access the public website. Visitors without the cookie will see a “coming soon” style of page.
You can customise the “coming soon” content, and you can change the way tokens work. Visit yoursite.com/?add_token to receive the token allowing you to see the site. To remove the limited access, simply disable this plugin.
By default, the token is “letmein”. So use these links: 
site.com?letmein 
site.com?takemeoff
This plugin is useful when you’re developing your site. You can work on your live web server without having your site open to the public.

Token Access

Limit access to the site to those with a cookie token.  Visitors without the cookie see a customisable "coming soon" style of page.

INVELITY

This plugin allows you to post a preview of any post for anonymous users before publishing it. Have you ever written a post with the help of someone who does not have access to your blog and needed to be able to view the article to comment on it before publishing it and do not want to have access to your blog’s administration? This add-on takes care of this by generating a URL.

Super Public Post Preview

Create and share link to anonymous users for preview any post before it is published.

Token Access vs Super Public Post Preview