Jon Aquino's YubNub is a social command line for the web. Try it here. At base level it's a customisable search query form. Much like existing web browser plug-ins. However, any user can add functionality to it, and there's lots of potential in adding a formal 'piping' (as in unix piping) framework, whereby you can envisage search queries like:

amazon hasselhoff | aws_get_titles | technorati_array_query | technorati_get_authors  

To give you a list of anyone who's blogged about any films david hasselhoff has ever been in (for possible contact and formation of Hasselhoff co-cast fanclub). Or simply:

google_img david hasselhoff | upload_to_flickr

Any web script triggered by a GET request can be declared as a YubNub command.

YubNub is a crucial, simple idea (cooked up as a 24 Hour challenge), and it's wholly in step with the net's slow morph from a set of interlinked documents to a global operating system running distributed, networked applications and services. It faces serious customer abuse/spam/security issues. It'll be interesting to see how it evolves in the coming weeks.

Also check Jon's Introspicious - intermediate tag analysis on the bookmarks you index at Delicious.