Paul Allen is back in the software market, with the launch of Xiant, a business that helps Outlook users organize their mail. Xiant is the latest in a growing industry of startups offering e-mail add-ons. Allen himself is also an investor in Gist, which combines e-mails from contacts with the latest news about them culled from blog posts, social-networking sites and Tweets. It raised $6.75 million in a round led by his investment firm, Vulcan Capital, last month. Another rival startup, Xobni has an Outlook plugin that pulls updates about a user’s contacts from Facebook, LinkedIn and other sites.

Vulcan, which is the only investor in Xiant, is playing up Allen’s hands-on participation in its launch, saying in a statement that it started “as a personal project to help Paul keep up with heavy e-mail traffic.” The company also says that it’s one of his “few forays into software” since he left Microsoft (NSDQ: MSFT) in 1983. Via Vulcan, Allen owns several sports teams, real estate in Seattle, as well as wireless spectrum. He’s also lost billions on his investment in cable company Charter Communications (NSDQ: CHTR), which filed for bankruptcy earlier this year.

Xiant files away a user’s messages based on the person’s past filing preferences. It also lets users track new messages based on their subject—so that people can follow a certain subset of messages without being distracted by all of their incoming mail. Release.

• Paul Allen-Funded Startup Gist Raises $6.75 Million In First Round
• Industry Moves: Paul Allen’s Vulcan Capital Replaces President