Share single topics / categories with unregistered users

[Heliosurge (Dan DeMontmorency)]

This plugin might be of interest to checkout

Advertise activity in a private category (discourse-category-lockdown)

This plugin allows you to restrict access to topic pages in a category. Topic titles will still show up in topic lists, search, user activity & digest emails. This is a great way to advertise the activity in a “members-only” category, which may charge for access. It IS NOT designed to keep the contents of the category 100% private - if someone is determined enough they will be able to piece together the content from search results. Each category has a couple of new settings in the Security tab…

Though Author said he’s not maintaining it.