Watchlist extension for Osclass display links on listing page that allows user to add that listing into its watchlist.
Only logged in users will be able to use watchlist feature, as watched items are stored only in database. Integration of plugin require to modify theme files to show watchlist button on ad page.
Watchlist feature is essential on most of classifieds websites as it gives opportunity to customers to save their preferred or favorite ads, watch their price or availability or simply have them close for purchase.
If you are looking for advanced functionality, make sure to look on premium Favorite Items Plugin that allows to store favorite items also to not logged users as well brings better utility functionality.
This addon is easy to install and require simple theme modifications to make it work properly, has also nice help page that clarify all needed changes.