On Tuesday evening Tim Cook gave an interview during the opening session of AllThingsD's D10 Conference. During that interview he spoke at some length about patent litigation, which he called "a pain in the ass." That very same day, it seems, a company called Cathas Advanced Technologies filed suit against Apple in U.S. District Court in Delaware. The suit accuses Apple of infringing on a patent owned by Cathas with its iOS Developer Program.
The patent in question, which can be read in detail here, was granted in August 2005 and deals with the creation and delivery of customized software to a customer via a web interface. Cathas's complaint (PDF) claims that Apple's iOS Developer Program infringes on the patent, though it does not specify how. Cathas is asking for "a reasonable royalty" along with interest and legal fees.
As you might have guessed, Cathas appears to be what they call a "non-practicing entity" (NPE), that is to say, a patent troll. Apple is not the only company against which Cathas has filed suit. On the same day that the Apple suit was filed, Cathas also filed complaints against Amazon, Expedia, Groupon, LinkedIn, LivingSocial, and Oracle, all in the same court, and all alleging patent infringement (though apparently of different patents).
Information about the company itself, though, is difficult to come by. A Google search for the company returned only results relating to these patent lawsuits, though Google helpfully offered an alternative search suggestion: