Huseyin Berberoglu

Allows users to add favorite posts. This plugin use cookies and database for 
saving data.
<ul>
<li>If a user logged in then favorites data will saved in database instead of cookies.</li>
<li>If user not logged in data will saved in cookies.</li>
</ul>
You can choose “only registered users can favorite a post” option, if you want. 
Also there is a widget named “Most Favorited Posts”. And you can use this template 
tag for listing most favorited posts;
Most Favorited Posts
If you use WP Super Cache you must add page (which you show favorites) URI to “Accepted Filenames & 
Rejected URIs”.
If you need support <a href="https://wordpress.org/support/plugin/wp-favorite-posts" rel="ugc">create a topic on support forum</a>
Please submit your pull requests to https://github.com/hberberoglu/wp-favorite-posts

WP Favorite Posts

Allows visitors to add favorite posts. This plugin use cookies for saving data so
unregistered users can favorite a post.

avrilmaomao

This plugin is based on “WP Favorite Posts”,and extends json api to provide access for mobile apps. 
Three methods are provided: 
wpfp/add 
 postid: required 
 cookie: optional 
wpfp/remove 
 postid：required 
 cookie：optional 
wpfp/lists 
 cookie ：optional 
The cookie param is the same as “JSON API USER” plugin used.
These methods support users not logged,if the client side can receive and send cookies.
code can be found at: https://github.com/avrilmaomao/wp-favorite-posts-extended

WP Favorite Posts Extended

wp-favorite-posts, reading list, post list, post lists, lists Requires at least: 3.5 Tested up to: 4.0 Stable tag: 0.1 Based on plugin "WP Favor …

WP Favorite Posts vs WP Favorite Posts Extended