Favorites is the original and premier entry and member saving add-on for ExpressionEngine! With robust and feature rich functionality and templating tags, you're able to accomplish a wide variety of things that go beyond the essentials of "saving and unsaving".
Favorites allows your members to save both entries and other members as favorites (and save notes!), multiple times too if they wish, using an Admin pre-defined set of collections. Favorites can then be updated, switched to different collections, or removed altogether. The sky's the limit on this, as this could be manipulated to simulate bookmarks, following members, upvoting content, photo light boxes, etc.
Included functionality for Favorites is:
NOTE: Documentation for Favorites 3.x can be found here.