Steve Ballmer just resigned from Microsoft's board of directors, six months after handing over the CEO reins to Satya Nadella and almost a year to the day after announcing his plans to retire.

Microsoft broke the news by posting Ballmer's letter to Nadella, and Nadella's very quick response, on its company news web site.

Three things stuck out about it:

Ballmer sees three important businesses for Microsoft's future:  He wrote "In the mobile-first, cloud-first world, software development is a key skill, but success requires moving to monetization through enterprise subscriptions, hardware gross margins, and advertising revenues. Making that change while also managing the existing software business well requires a boldness and fearlessness that I believe the management team has." (Itals mine.) It's clear that Nadella is full speed ahead on enterprise subscriptions via Azure, Office 365, and other services. But he hasn't said as much about hardware -- although Stephen Elop hinted that the role of Nokia hardware within Microsoft would be more of a showcase for Microsoft software and services than an end in itself. And Nadella has said nothing about advertising, although he did lead Microsoft's search engine for several years, so certainly has experience there.

He's still the number-one shareholder.  "I hold more Microsoft shares than anyone other than index funds and love the mix of profits, investments and dividends returned in our stock. I expect to continue holding that position for the foreseeable future." So while he may not be an active boardmember, he still holds more voting rights than any individual, including cofounders Bill Gates and Paul Allen. That means if he strongly disagrees with Microsoft's future direction, he still has some influence -- for instance, if things get really bad he could help push for new boardmembers.

The letter was posted to his Twitter account and OneDrive.  Oddly, Microsoft's PR director Frank X Shaw posted a link to Ballmer's tweet about his stepping down. This seemingly confirms that the @stevebmicrosoft account is really Ballmer's though he hasn't tweeted much. It also shows that Ballmer still bleeds Microsoft blue -- posting his letter to Microsoft's cloud service rather than, say, a personal blog or web site.

Say what you will about it, the Ballmer era at Microsoft is truly over.