Continuum links
With his new blog, Functioning Form, Luke Wroblewski has created a nifty bit of functionality he calls continuum links. Luke intends his blog to re-examine and expand upon earlier posts as he develops ideas and concepts. This organic approach is not catered for by the chronological (or even categorical) organisation of blogs, so Luke is adding automatic cross-referencing at the end of any post which is referred to by another.
Like many good ideas, this is simple and obvious, yet I’ve never seen it used elsewhere, although it is essentially a localised version of Trackback.