NutshellMail opens to the public, e-mails you the highlight reel from all social networks

It’s pretty much compulsory now to be on a couple of social networks. But how do you keep track of 700 friends, 500 Twitter accounts, 150 LinkedIn connections and a couple MySpace friends?

One of the startups from Facebook’s incubator fbFund, NutshellMail, is trying to provide an answer to the problem, and it opened to the public today. It sends you an e-mail digest of a select number of updates from all your social networks — an approach that makes it the polar opposite of companies like Tweetdeck and Seesmic, which supply a constant, almost-intravenous drip of status updates every minute.

NutshellMail is designed as a productivity tool for the casual user. Instead of getting a couple dozen Facebook or Twitter-related e-mails every day that you reply to piece by piece, you can get a single e-mail with all that information and address it in one go without being interrupted by new e-mail.

In the new version, NutshellMail lets you comment on Facebook posts, share stories, write on walls and update your status directly via e-mail. You can also get a digest of updates from Facebook pages and Twitter lists now.

NutshellMail’s business model could be quite similar to other e-mail newsletters out there like Thrillist or Daily Candy, which do advertising and branded takeovers. But it could also do more advanced types of interest-targeting based on the kinds of messages you receive (similar to how Gmail provides advertising space alongside e-mails based on keyword matches).

It could be a very helpful tool, but it could also make its filtering technology more sophisticated. Right now, it takes excerpts of the Twitter data stream — like the 20 most recent updates from your regular feed — and then piggybacks off Facebook’s more complex filtering algorithms for finding the most engaging status updates. In an ideal world, it would somehow automatically figure out the 20 most important updates out of several thousand from all your social networks instead of the most recent ones.

The company raised a $600,000 seed round this year and boasts a 70 percent retention rate after 30 days of use.