Lots of people can get a hold of you in multiple ways, and sometimes it's all too much. Gist grabs your Gmail or Outlook messages, Linkedin, Facebook and Twitter pings and sorts it by contact and importance.
Gist is really just a series of smart filters for the massive contact list you've built up in your email and social network services. The organiser looks to see how often your contacts appear in news articles, how many times you've gone back and forth with them, what companies they're affiliated with, and other criteria to assign an importance rank, which you can then apply to your ultimate inbox. That "importance" rank can be adjusted, and good thing, too—Gist thinks senders from Google.com are my most important contacts, but only because calendar.google.com mails my schedule every day, which is filtered to be auto-archived if there's nothing in it.
If you tend to look at your messages contact-by-contact rather than last-in, first-out, Gist is just the tool for you. It's a free service (at least while in beta), and requires authentication with other services to pull in data, unless you happen to have all your social back-and-forth in tidy CSV files.