I just installed Xobni (inbox backwards) and I found it very useful. I can’t really put a word on the application but it’s like placing Google search, analytics, but for your email. It’s cool!
Xobni extracts bits of useful information on your emails and place them conveniently on the sidebar (if you are using Outlook). Some of them are phone numbers, attachment discovery, threaded conversations, related persons, email count per person and ranking, and more.
There are a lot more features but I’d let this page tell you more about it.
We were developing something similar (but online version) under the codename Udeko (now known as Xackup) almost 4 years ago. It never came to production because we had to shift to other business models – backup.
I still personally like to finish that sometime soon if and when time permits and if my team is still up for it.