content is edited by a single/few author and accessed by urls. each site links to other sites they like, in a 'cool links' section. or via a web ring.
examples: geocities, tripod, just hosting a site yourself, etc
content is grouped into topics, which is edited by many users. some one creates a forum topic, and users post messages in that topic. I group wiki in with forums, because the data model is similar - collective edits to a shared resource, although, the way it is presented is quite different.
examples: wikipedia, github issues, blogs with comments.
blogs blend the experience of a forum with a static site. realtime chat (example: irc, meatspac.es), is like an ephemeral version of a forum.
content is grouped into user feeds. each user creates posts, which are shown to other users who "follow" them. feeds my not be available to the public internet, requiring users to login first.
examples: twitter, facebook, linkedin.
some sites, like youtube have open comments, but also have feeds where you can subscribe. even github has "follow", but I think the emphasis on it is fairly low (i never look at it) and so github is used more like a blog.
Each of these have differing levels of interactions between users, and have differing levels of work from each user to create content. comments are very cheap - posting a blog is a lot of work. twitter is all comments. making a youtube video is hard, but posting a comment is very easy. in a static site, all the users work fairly hard.