For my site, I want to let users subscribe to the post category or post tags. That is under every post there will be a subscription form with choices to select from categories and tags attached to that post. Very similar to this page: http://www.buzzsugar.com/Catching-Fire-Pictures-26818344
Just scroll down and look for the section "popsugar alert".
I have searched a lot, bit couldn't find resource or plugin that can help me.
Best will be the form will be added in the edit post page with the default categories and tags, and editor should have a choice to include or exclude manually. Help appreciated.