RSS Cloud
ma.tt/2009/09/rss-cloud
From the page
Saved with the link. Notes from 2007 to 2016 are mostly the page's own words, so this is probably an excerpt.
RSS Cloud support has been turned on for WordPress.com and you can download a plugin for WordPress.org. Both are first iterations and will continue to be improved over the next few weeks, and I’ll be at the RSS Cloud meetup on Wednesday.