Better collaboration software

I've recently read an article on Central Desktop at this site and saw an invitation to comment on it in this forum, so here I come :)
Central Desktop looked like a powerful tool for me at first, but then it turned out that there's still some place for improvement. What they lack is full incorporation of email into their product. Email is my business bread, so I wanted a tool that will combine my email correspondence with clients and my project work. Wrike suits http://www.wrike.com/ me much better. I issue a task for one of my team members, send a copy to my client and to wrike’s address. Collaboration model is so simple, nobody has to learn anything. My clients love it.