Mind mapping and other collaborative planning and brainstorming tools.

http://www.mindomo.com/
http://bubbl.us/
http://www.mindmeister.com/
http://www.imindmap.com/
http://freemind.sourceforge.net/wiki/index.php/Main_Page

There's more - I found a lovely one with hexagons - can't find it now... SHEESH!!!