Another one of Twitter's founders, Biz Stone, will leave the start-up.

FORTUNE -- In the continuing game of musical chairs among executives at Twitter, another of the company's founders is leaving. In a June 28 blog post, Biz Stone announced he will join founder Evan Williams, who left the CEO position last fall, and Twitter's former vice president of product Jason Goldman, who left the company abruptly in December. The trio will be relaunching the Obvious Corporation -- the business that initially hatched Twitter -- to, as Stone writes, develop systems that "help people work together to improve the world."

Of his current work at Twitter, Stone writes: "I've decided that the most effective use of my time is to get out of the way until I'm called upon to be of some specific use." Dick Costolo remains CEO of Twitter.

Fortune chronicled the management challenges facing Twitter in the April cover story "Trouble@Twitter:"

Trouble @Twitter
Boardroom power plays, disgruntled founders, and CEO switcheroos are clipping the wings of this tech high flier.

By Jessi Hempel, senior writer

FORTUNE -- In March, shortly after Jack Dorsey went back to work for Twitter, the company he co-founded four years ago, he did a Q&A session with an entre­preneurship class at Columbia Business School. As students tapped away on their laptops (were they sending tweets?), Dorsey, 34, answered questions about his commitment to his new gig as Twitter's product chief. Dorsey, after all, is also CEO of Square, a hot payments business, and he returns to Twitter after a rocky run as its CEO -- the board demoted him in 2008. (Co-founder Evan Williams took over and held the job for almost two years; then operating chief Dick Costolo assumed the top job.) "Seems like a revolving door," mused the interviewer.

Dorsey laughed lightly and replied, "You know, we're just individuals. We're just humans running these companies." And he compared managing a startup to, of all things, supervising a theater company.

There's no shortage of drama at Twitter these days: Besides the CEO shuffles, there are secret board meetings, executive power struggles, a plethora of coaches and consultants, and disgruntled founders. (Like Williams. The day after Dorsey announced his return to the company -- via tweet, naturally -- Williams quit his day-to-day duties at the company, although he remains a board member and Twitter's largest shareholder, with an estimated 30% to 35% stake.) These theatrics, which go well beyond the usual angst at a new venture, have contributed to a growing perception that innovation has stalled and management is in turmoil at one of Silicon Valley's most promising startups, which some 20 million active users rely on each month for updates on everything from subway delays to election results -- and which a growing number of companies, big and small, seek to use to market themselves and track customers.

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