I tried ReactOS and it's unbearable to use, but what it's attempting is genuinely brilliant

ReactOS is a FOSS project that aims to recreate Windows NT functionality from scratch using clean-room reverse engineering, with no proprietary components. Despite nearly 30 years of development, it remains an alpha-stage OS that is largely unusable for daily tasks — the newest available browser is Firefox 52 ESR, performance is poor, and many apps are broken. However, the project is technically fascinating and continues to receive updates, with stable release 0.4.15 and nightly builds toward 0.4.16. It's worth knowing about for its ambition and potential to reduce Windows dependency, even if it's not ready for practical use.