This website uses the P2 theme by Automattic. I use it because its so quick and easy to post with (though I wish it were easier to add a link to text). A company altered the P2 theme to make it look like Basecamp, the online project management and collaboration software by 37 Signals. Its unfortunately not up to date right now, as P2 has come a couple versions since they did it, but hopefully they’ll update their variation soon. Get it here: http://templatic.com/news/gtd-%E2%80%93-private-blog-theme-for-teams-to-collaborate
Also, if you wanted to take it a step further, here’s a plugin that allows you to manage projects, assign tasks, and more: http://wordpress.org/extend/plugins/wp-project/. Unfortunately it hasn’t been updated in a while, so I’m not sure if it works with the most recent versions of WP.