Secret Metafilter is a web app that highlights Metafilter discussions that are still active on older posts.
It is a Google AppEngine app that periodically scrapes the past month of Metafilter and renders an HTML display of the most recent discussions that are still active.
You can see it running at http://secretmefi.appspot.com/.
$ make
$ virtualenv env
$ env/bin/pip install NoseGAE argparse distribute lxml nose wsgiref
$ env/bin/python env/bin/nosetests --with-gae --gae-lib-root=/usr/local/google_appengine --without-sandbox