This is a Messaging Framework to allow message sending in a channel independent way. It will provide a common API for message composition and sending while allowing plug-ins for multiple messaging methods.
When using this framework, you won't send e-mails to users anymore. You will send them 'messages' and they will decide how they want to get them delivered, that may be by mail, IM, SMS, depending on user's preferences...
Drupal 7 upgrade
Some limited funcionality has been upgraded.
Development is back on Drupal git repository.
Graphviz Filter is a fun little filter that treats input text as GraphvizDOT syntax, converts it using Graphviz tools to the requested format(s) and renders it in HTML. It's useful to quickly create graphs dynamically from within Drupal nodes. A particularly exciting application is to create an input format consisting of PHP code followed by Graphviz Filter, thereby allowing one to write code that outputs a DOT file, which is then rendered to HTML. For example, one could create a visual taxonomy tree with nodes hanging from the terms, and each visual node would be clickable (using the URL Graphviz attribute) to point to the actual Drupal node. Stuff like that!
Thanks to varienne for the great documentation (in the Resources section below)!