Linux is a very popular open-source Unix-like operating system. Open-source Unix-like operating systems that are not based on Linux and are still actively developed. They are
- FreeBSD
Focus: Performance, advanced networking, storage
Use Cases: Servers, firewalls, storage appliances (e.g., TrueNAS) - OpenBSD
Focus: Security, correctness, simplicity
Known for: Secure-by-default policies, clean codebase - NetBSD
Focus: Portability — runs on almost any architecture
Use Cases: Embedded systems, research, legacy hardware - DragonFly BSD
Focus: Performance, advanced file system (HAMMER2), scalability - illumos
Descendant of: OpenSolaris (which was derived from UNIX System V) - OpenIndiana
Goal: Desktop/server OS based on illumos - SmartOS
Focus: Cloud-native virtualization with zones, ZFS, DTrace - MidnightBSD
Fork of FreeBSD, focused on desktop use - Darwin
Apple's open-source core of macOS (not a complete OS itself)
Basis for macOS and iOS
Most those operating system are intended to run as server connected directly to internet with advance stability and security.
