μ–kernel

Microkernels are operating systems that outsource the traditional operating system functionality to ordinary user processes while providing them with mechanisms requisite for implementing it. Microkernel-based operating systems come in many different flavours, each having a distinctive set of goals, features and approaches. Some of the most often cited reasons for structuring the system as a microkernel is flexibility, security and fault tolerance. Many microkernels can take on the role of a hypervisor too. Microkernels and their user environments are most often implemented in the C or C++ programming languages with a little bit of assembly, but other implementation languages are possible too. In fact, each component of a microkernel-based system can be implemented in a different programming language.

Here is a list of active free, open source microkernel projects. If your project is missing, please let us know!

Escape

A UNIX-like microkernel operating system, that runs on x86, x86_64, ECO32 and MMIX. It is implemented from scratch and uses nearly no third-party components. To fit nicely into the UNIX philosophy, Escape uses a virtual file system to provide drivers and services. Both can present themselves as a file system or file to the user. (github.com/Nils-TUD/Escape)

F9

An experimental microkernel used to construct flexible real-time and embedded systems for ARM Cortex-M series microprocessors with power efficiency and security in mind. (github.com/f9micro)

Genode

A tool kit for building highly secure special-purpose operating systems. It scales from embedded systems with as little as 4 MB of memory to highly dynamic general-purpose workloads. (genode.org)

HelenOS

A portable microkernel-based multiserver operating system designed and implemented from scratch. It decomposes key operating system functionality such as file systems, networking, device drivers and graphical user interface into a collection of fine-grained user space components that interact with each other via message passing. (helenos.org)

GNU Hurd

The GNU project's replacement for the Unix kernel. Notable features include the distributed virtual filesystem that is used as namespace for system services, high degree of application compatibility by shipping the GNU C library, and the goal of being a general purpose operating system. (hurd.gnu.org)

L4Re

Forms the foundation for application development and interaction on the Fiasco.OC microkernel. It consists of basic services such as program loading and memory management. L4Re also provides the environment for applications, including libraries and process local functionality. (l4re.org)

A microkernel-based system for heterogeneous manycores, that is developed as a hardware/OS co-design at the TU Dresden. It aims to support arbitrary cores (general purpose cores, DSPs, FPGAs, ASICs, ...) as first-class citizens. This is achieved by abstracting the heterogeneity of the cores via a new hardware component per core, called data transfer unit. (github.com/TUD-OS/M3)

MINIX 3

A free, open-source, operating system designed to be highly reliable, flexible, and secure. It is based on a tiny microkernel running in kernel mode with the rest of the operating system running as a number of isolated, protected, processes in user mode. (minix3.org)

The Muen Separation Kernel

The world’s first Open Source microkernel that has been formally proven to contain no runtime errors at the source code level. It is developed in Switzerland by the Institute for Networked Solutions (INS) at the University of Applied Sciences Rapperswil (HSR). (muen.sk)

NOVA Microhypervisor

A research project aimed at constructing a secure virtualization environment with a small trusted computing base. NOVA consists of a microhypervisor and an unprivileged multi-server user environment running on top of it. (hypervisor.org)

Redox

A Unix-like operating system written in Rust, aiming to bring the innovations of Rust to a modern microkernel and full set of applications. Redox isn't afraid of dropping the bad parts of POSIX, while preserving modest Linux API compatibility. (redox-os.org)

seL4

A high-assurance, high-performance microkernel developed, maintained and formally verified by NICTA and owned by General Dynamics C4 Systems. It is a member of the L4 family of microkernels, and is the world's most advanced, highest-assured operating-system microkernel. (sel4.systems)