Darwin-based systems – Open-source Unix-like core of macOS/iOS, with community projects and derivatives
OpenDarwin – Historical community-led Darwin OS project (discontinued around 2006, archived on Wayback Machine). Predecessor to efforts like PureDarwin.
PureDarwin – Community project to make Darwin bootable and usable standalone (successor to OpenDarwin). Active research ongoing, minimal system without GUI, latest test builds from 2018+, developer-focused.
ravynOS (formerly RavenOS?) – Early-stage open-source OS based on Darwin/FreeBSD/Apple code, aims for macOS app compatibility and similar experience without hardware lock-in. Pre-alpha, active development on GitHub.