Linux is a clone of the Unix kernel, written from scratch by Linus Torvalds with assistance from a loosely-knit team of hackers across the Net. It aims towards POSIX and Single UNIX Specification compliance. It has all the features you would expect in a modern fully-fledged Unix kernel, including true multitasking, virtual memory, shared libraries, demand loading, shared copy-on-write executables, proper memory management, and TCP/IP networking.
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.
Endian Firewall is an all-in-on Linux security distribution that turns any system into a full-featured security appliance. It features a stateful packet inspection firewall, application-level proxies for various protocols (HTTP, POP3, SMTP), anti-virus support, virus and spam filtering for email traffic (POP and SMTP), content filtering of Web traffic, and a "hassle free" VPN system based on OpenVPN.
EV-OS is an operating system which runs in real mode on the x86 platform. The system must be booted and run from floppy disk. The user interface is command-line based. Application programs must be prepared for operating system. EV-OS application programs can be developed under the Windows operating system, and a special tool is used to transfer files from Windows to EV-OS. EV-OS is written in assembly and the transfer program is written in C. The downloadable package contains an executable image file, the source code of the operating system, and some installation documentation.
SOSSE (Simple Operating System for Smartcard Education) is a free smart card operating system. It is implemented in C and assembler for the Atmel AVR smart cards (Funcard, PinkCard, Jupiter). The aim of this project is to provide something like Linux for smart cards, which is a market full of NDAs. SOSSE should make it possible to learn about smart cards, and to implement and test your own ideas.
OpenSDE is a kit for creating customized operating systems based on GNU/Linux. OpenSDE has an easy configuration tool which allows anyone to put together their own GNU/Linux distribution that addresses their specific needs. OpenSDE supports over 2400 software packages and the number is still growing.
System and Process Monitor in Java provides a JNI (Java Native Interface) implementation for monitoring global system resources and processes (outside JVM) via a unified (cross-platform) interface. The Java interface and all native libraries are compiled into a single JAR and are loaded transparently on any architecture upon request. It should be easy to embedd this code into your Java applications, either as a separate JAR or as one single application archive.