From dual-booting to WINE, free software has always struggled to provide a solution for running Windows applications. However, few of these efforts have been more ambitious than ReactOS, a free-licensed implementation of Windows. The project has been at work since 2006 and, in February 2016, ReactOS finally released its first alpha version, after a decade of difficult and necessarily cautious development.
ReactOS, the project aiming for binary compatibility with Microsoft Windows (Server 2003), now has Btrfs file-system support.
While there's just a primitive Btrfs driver for Windows, ReactOS has already gained native Btrfs file-system support.