Minimalistic system — by design has a tiny attack surface Lacks multi-user accounts or advanced permissions
Technically not a standalone OS kernel, but a network operating system layer installed on top of MS-DOS or Windows
Monolithic with distributed system extensions
Beautiful Aqua GUI with advanced graphics (Quartz, Metal)
MenuetOS (also known as MeOS) Tiny footprint: Core OS fits on a 1.44 MB floppy (still with GUI, network, and apps)
MINIX is a historically significant OS that proved the practicality of the microkernel design and served as the catalyst for the world's most popular kernel, Linux
Multiplexed Information and Computing Service
Novell NetWare Monolithic, multitasking real-mode (in early versions), later protected mode
Plan 9 from Bell Labs
ReactOS
Originally Acorn Computers, now maintained by RISC OS Open Ltd
SerenityOS Community-led project (founded by Andreas Kling)
