Microsoft’s devouring of our favorite mobile apps continues today with the acquisition of 6Wunderkinder, makers of popular task management app Wunderlist.

The buyout, which comes just four months after Microsoft acquired Sunrise, will help the software continue its mission to reinvent productivity in a mobile-first world, it says.

In just five years, Wunderlist has amassed a whopping 13 million users who have created more than 1 billion to-dos. It serves users on Android, iOS, Windows Phone and desktop platforms, and with the power of Microsoft behind it, it promises to get bigger and better.

“Over the next few months as Wunderlist becomes a part of the Microsoft family, we’ll introduce a host of new features, continue growing the ecosystem of partner integrations and progress in delivering Wunderlist to billions of people,” 6Wunderkinder says.

For the time being, however, Wunderlist will continue in its current form, and will be managed by the same team that created it. Microsoft also promises that it will remain free in existing markets, and prices will not change for those paying for Wunderlist Pro and Wunderlist for Business.

Microsoft hasn’t disclosed how much it paid for 6Wunderkinder, but a recent report from The Wall Street Journal suggested the fee could be between $100 million and $200 million.

“I couldn’t be more proud of my team,” 6Wunderkinder CEO Christian Reber said in a blog post today.

“I started this company with a dream. My team turned it into a reality. Together we have created an award winning beautiful and simple to-do list that is powered by a real-time sync architecture, unlike any other.”

• SourceWunderlist
• ViaMicrosoft