Nuttx is a real-time embedded operating system (RTOS). It has a small footprint that is usable in micro-controller environments. It is fully scalable from tiny (8-bit) to moderate embedded (32-bit) systems. It also aims to be fully compliant to standards, to be fully real time, and to be totally open.
Warewulf is an operating system management toolkit designed to facilitate large scale deployments of homogeneous and heterogeneous systems on physical, virtual and cloud based infrastructures. Originally, the Warewulf project pioneered the concept of stateless computing in HPC, setting the standard for large-scale cluster provisioning. It provided two functions, provisioning and monitoring but the two functions did not communicate within Warewulf itself, nor was it possible to hook other functions directly into Warewulf itself. Today, Warewulf is more than just a basic provisioning and monitoring solution as it now implements an abstract, object-oriented data store and a modular interface that facilitates a highly extensible, customizable feature set. Current and planned modules include monitoring (operating system, services, filesystems, etc.), provisioning, power management, user management, configuration management, event/trigger handling and notification, scheduler integration, cloud services (both local and remote), etc.
Contiki is an open source, highly portable, networked, multi-tasking operating system for the Internet of Things. Contiki includes a multitasking kernel, a TCP/IP stack and a set of application programs, and a low-power radio communication stack. It is written in C and designed to be very small: it runs comfortably in a few kilobytes of RAM.
MikeOS is an operating system for x86 PCs, written in assembly language. It is a learning tool to show how simple OSes work, with well-commented code and extensive documentation. It features a text-mode dialog-driven user interface, a file manager and machine code monitor, and over 60 system calls for use by third-party programs.
Rocks is a complete "cluster on a CD" solution for x86 and IA64 Red Hat Linux COTS clusters. Building a Rocks cluster does not require any experience in clustering, yet a cluster architect will find a flexible and programmatic way to redesign the entire software stack just below the surface (appropriately hidden from the majority of users). Although Rocks includes the tools expected from any clustering software stack (PBS, Maui, GM support, Ganglia, etc), it is unique in its simplicity of installation.
MirBSD originated as a patch set against OpenBSD-current, an ultra secure operating system and NetBSD derivate, and has since also incorporated changes from NetBSD, a 4.4BSD-derived ultra portable operating system. It features bugfixes, code removal for the sake of simplicity, and feature enhancements over stock OpenBSD as well as a much more up-to-date GNU toolchain, careful integration of patches from other projects (such as KAME), and many improvements. It works on the Intel Pentium and some 80486 machines with more than 32 MiB RAM and the SPARC, and a port to the PowerPC Macintosh is in preparation.
HelenOS is a microkernel-based multiserver operating system designed from scratch. By decomposing the operating system functionality into tens of isolated but intensively communicating userspace servers, it provides a computing environment that has several virtues such as flexibility, increased robustness, well defined explicit interfaces, and smaller complexity of individual components. HelenOS does not aim to be another clone of Unix or some other legacy system and is not POSIX-compliant (even though it may seem POSIX-similar at times). Instead, the goal has been to design it according to what is the most elegant and right thing to do. What makes HelenOS unique among the other multiserver operating systems is its multiplatform and multiprocessor microkernel. It will run on seven different processor architectures ranging from a 32-bit uniprocessor little-endian ARMv4 to a 64-bit multicore big-endian UltraSPARC T1.
DragonFly belongs to the same class of operating systems as other BSD-derived systems and Linux. It is based on the same Unix ideals and APIs and shares ancestor code with other BSD operating systems. DragonFly is differentiated from other operating systems in its class by, among others, the HAMMER file system, Virtual Kernels, swapcache, and the pervasive use of soft token locks. DragonFly provides an opportunity for the BSD base to grow in an entirely different direction from the ones taken in the FreeBSD, NetBSD, and OpenBSD series.
flashboot for OpenBSD is a set of makefiles, scripts, and support tools to build an OpenBSD image suitable for booting from read-only media, such as flash memory. The default image (smaller than 5Mb) is an image for a firewall/router with support for IPsec, SSH, IPv4 and IPv6 packet filtering, DHCP (client and server), and PPPoE. This image may be further trimmed or extended by editing the packing list files included in the distribution.