Tag the Web! Synopse allows you to submit tags of URLs to the
Synopse search engine (http://www.synopse.net/).
The "synopse," concept is an alternative way of search/discover Web content and connect contextually related websites. User generated meta data aggregation could be a potentially strong alternative/addition to automated/spider indexing of the web.
A dissertation discussing the pros/cons of user generated meta data aggregation in the context of web search and discovery as well as a more detailed description of "synopse," can be found in my Master of Arts dissertation: