onetruefanBoulder, Colo.-based OneTrueFan today announced its new service to help website publishers connect with their most loyal readers.

If that sounds familiar, it’s because Badgeville, a startup making similar promises, launched earlier in the afternoon. Both of them demonstrated at the TechCrunch Disrupt conference. But OneTrueFan’s approach is a bit different. It offers a toolbar for users to “check in” when they’re reading an article, similar to what users do in location startup Foursquare. They then share articles on social networking sites and elsewhere. By building up check ins and shares, a reader can be declared the “one true fan.”

Co-chief executive Eric Marcoullier said that nailing the user experience for the toolbar is key to beating competitors, and that’s something the OneTrueFan team (which previously co-founded MyBlogLog, the blog social network acquired by Yahoo) has been perfecting for a while.

Google Ventures’ Joe Kraus, one of the judges at the conference’s Startup Battlefield, said that the market is too crowded, and that these competing startups will be killing each other off over the next couple of years, with one winner left standing: “You can feel the venture fratricide coming.”

Kraus added that while he’s convinced that this “Foursquare for websites” concept will eventually show up on most sites, he’s not sure anyone has figured out how to build a real company around it.