Token Content Access allows you to restrict access to individual nodes using URL tokens. In order to view protected nodes, users must provide a unique token via the URL. This allows nodes to be published and viewable to anonymous users (for instance with a special link from an email campaign) but not visible to the public at large. It also automatically hides any TCA-protected content from Views results.
There is overlap between this module and Access Unpublished (in that they both generate tokens to view content) but this module addresses a slightly different use case, where the only access to published content is using a token.