Chrome: Graph Your Inbox is a fascinating Chrome extension that takes Gmail search queries and returns a graph displaying email frequency over time. It may not sound sexy, but it can expose all sorts of interesting things about your communication.
If you're a data nerd, it's actually all kinds of addictive. For example, a quick batch of
from: searches of friends' names provides a fascinating (to me at least) graph of your interactions with friends over time. More specifically, here's a sample use case I found particularly interesting:
A quick search turning up all the emails sent from my significant other show email frequency progressing steadily during a time during which she was increasingly dissatisfied with her job. When she left her job, the frequency halved.
Those sort of personal history searches are surprisingly fun, but you could also use the tool for more practical productivity purposes too. Say, for example, that you've got the sneaking suspicion that you're wasting more time than ever on Facebook, or that your work inbox has grown steadily out of control with unnecessary email. While it couldn't interpret the value of all your email, Graph Your Inbox could provide a quick analysis of email frequency so you can quickly determine if it's been rising in general. If you see a trend and you want to examine it more closely, you can click a data point to open your Gmail inbox to the messages sent during that time.
Graph Your Inbox is a free extension for Gmail users, currently works only with Chrome. It doesn't save any of your personal information, and it doesn't require your email or password.