ReactOS Has Been Steadily Improving As An Open-Source Windows Implementation
ReactOS over the course of 2020 saw shell improvements, usability enhancements to its application manager, upgrading to GCC 8.4 and CMake 3.17 as its central build components, progress on Clang compiler support (albeit still not yielding bootable binaries yet), the new storage stack was merged, Kernel-Mode Driver Framework support, enhancements to its memory management code, plug-and-play enhancements, and more.
But at the start of 2021, ReactOS is still driving i386 as its primary platform while their AMD64 support is still a work-in-progress. Much of their AMD64 support has been merged but the graphical interface still has problems and other issues. A port to the original Xbox also continues to be worked on as well as a NEC PC-98 port.
Looking to the year ahead the developers hope to work more on forward compatibility subsystem for Windows Vista and later application support, printing, CRT and standard library improvements, and more AMD64 and SMP work.
More details on this ongoing "open-source Windows" work via the project's annual recap on ReactOS.org.