Microsoft has reached an agreement to buy start-up 6Wunderkinder, known for its popular to-do list app called Wunderlist, for between $100 million and $200 million, The Wall Street Journal reported.  

The purchase is part of Microsoft's attempt to bolster its range of mobile apps. It recently launched the mobile version of Microsoft Office and has also bought two other companies that make mobile applications, San Francisco-based Acompli and a startup based in New York behind the Sunrise mobile calendar app. The company rebranded Acompli as the new versions of Outlook available for Anroid and iOS, but it hasn't done much yet with Sunrise's calendar app.

The Berlin-based startup 6Wunderkinder has the backing of several investors such as Sequoia Capital, an American venture-capital firm, as well as Earlybird Venture Capital and European VCs Atomico.

Wunderlist is more than just a simple to-do-list app, allowing users to share tasks and lists with other users over the Internet. The application can be used to do everything from managing grocery lists to scheduling tasks for coworkers.

Microsoft's strategy seems to revolve around popular cross-platform productivity apps that not only run on Windows devices but also on Android, iOS and Mac platforms. The goal is to attract users by offering great apps and services through Microsoft, hoping that some of those users will eventually make the switch to Windows devices, according to Business Insider.