Children of WordPress: How many are there?

Until very recently I only knew of BuddyPress.  Now it seems like I'm constantly running into plugins that make cool variations of WordPress.  I thought it would be handy to put a list together as a resource.

BuddyPress--turns WordPress into a social network. 

bbPress--forum software.  Now bundled into BuddyPress.

CollabPress--project management plugin.

VideoPress--as far as I know, you need to have a WordPress.com account to get this.

PodPress--adds features to make a WordPress site a broadcasting platform.

BackPress--a PHP library of core functions that could be used to build prototype web apps.  There's a video of a presentation called Rapidly Prototyping Web Applications Using BackPress.  I was a bit underwhelmed, though.  I think it would just be better to go straight to a web framework.

TwentyTen CRM--uses WordPress as a customer relationship management tool.  Thanks to TechHui member Jon Brown for mentioning this in my last post about WordPress for collaboration.

Are there any other helpful variations of WordPress you know of?  What was your experience using them?