Ottocat was a startup that launched a tool in May of 2013 aimed at making app discovery through the App Store easier by cataloging specific subcategories — that is until Ottocat's website abruptly went down in October of 2013. As TechCrunch reports, there was no evidence of an acquisition by Apple until a patent application was discovered linking an Ottocat co-founder to Apple:

There is precious little evidence of the connection between Ottocat and Apple — no LinkedIn employment changes, no announcements to Ottocat users — save for one thing. One of Ottocat's co-founders, Edwin Cooper, authored a patent that was granted to Apple as the original assignee. It looks like that patent was filed by Cooper as an employee of Apple. That patent, for a "System and Method for Divisive Textual Clustering by Label Selection Using Variant-Weighted TFIDF" pertains to the kind of technology used both by Ottocat and Apple's explore feature.

As TechCrunch notes, Apple later announced the Explore tab for the App Store in mid-2014, which operates much like Ottocat did by providing a way to whittle down a search by increasingly specific categories.

Source: TechCrunch