Push Pop Press
Jobs reportedly delivered an ultimatum to Matas that resulted in the company selling itself to Facebook as a talent-based acquisition that abandoned its allegedly tainted ebook apps business model.
Because Push Pop Press planned to deliver its version of ebooks as native iOS apps, Apple’s iOS App Store was ultimately the sole potential distributor the finished work Push Pop Press would have created, giving the company little leverage in arguing around any IP claims by Apple.
In other words, they would be tried by the App Review Board rather than a court of law.
Update (2012-01-21): John Gruber:
Jobs more or less warned Push Pop Press that Apple was going in the same direction, in a big way. A competitive warning, not a legal threat.