What's Trello ?
Trello is a really nice application to manage about everything you want. The GUI is really cool and simple to use, we are actually testing it in my company and we have a very good first feeling. If you want to discover more, don't hesitate to watch the presentation video and give it a try at Trello website.
Trello provides a very nice notification system, instead of spamming you with mail everytimes something happens, it detects your activity on the site and sends you mail only when you're offline / idle. The only thing I miss is the hability to see if I have missed notification in my pinned tab. I remembered of a good userscript for GMail allowing to display the number of unread emails. As I have no experience in GreaseMonkey scripts, I used the previous one as a learning base and did a script allowing to see the number of missed notification (from 1 to 9, and displaying a + if it exceeds 9).
You can see it in action in the blog post picture next to GMail pinned tab in Chrome.