Warning: this webpage loads many processor-intensive animations. It might break your browser and probably you will have to close browser window (tab) after use.
The first visualization is made by Erik Zachte and available at stats.wikimedia.org.
The animation (embedded below) shows 4 aspects of the development of different Wikipedias in different languages (en, it, fr, …): X-axis: Age of a project, Y-axis: Number of articles per project, Circle size: Number of editors per project, Color: Maturity of content (blue=mostly stubs, violet=mostly larger articles)
Interactive version, all projects (requires Firefox 3+, Safari 4+ or Chrome)
Static version, Wikipedia only (8 Mb Flash)
I embed them here but you can check Matt’s post for more details and better visualization.
Activity — a rippling visualisation of comment activity on the wiki. Based loosely on the Apple Arabesque screensaver.
Comments — a falling bar-graph visualisation of comments by blogpost. Based very much on a Flash visualisation by Digg, but reimplemented in JS (this is about blog and not wiki).
Contributors — a tree graph visualisation linking commenters and blog post authors. (this is about blog and not wiki)