You've probably heard by now, Jack Dorsey, the co-founder & CEO of Twitter, resigned effective yesterday. The news had been rumored yesterday morning, with CNBC reporting that Dorsey's departure was imminent. By afternoon, Dorsey had confirmed it, tweeting an email he sent to employees announcing that he was stepping down.Dorsey's email mentioned his successor, Parag Agrawal, and thanked employees for their ambition and potential. He even mentioned Bret Taylor, who is the President and COO at Salesforce, and is now Chairman of Twitter's Board.