ReactOS
http://www.reactos.org/
USER-CENTRIC IMPROVEMENTS
-ext2 read/write and NTFS read support
-New explorer shell and theme support
-SerialATA support
-Sound support
-USB support
-VirtualBox and VirtualPC support
-Wireless networking
DEVELOPER-CENTRIC IMPROVEMENTS
-CMake support for GCC and MSVC compilation
-Compilation times significantly improved
-GDB remote debugging interface for kernel debugging
-WinDBG support