Fiwix is an operating system kernel based on the Unix architecture and fully focused on being Linux compatible. It is designed exclusively for educational purposes, so the kernel code is kept as simple as possible for the benefit of students. It runs on the 32-bit x86 hardware platform, and is compatible with a good base of existing GNU applications.
The MultiAdmin security framework kernel module provides a means to have multiple "root" users with unique UIDs. This bypasses collation order problems with NSCD, allows you to have files with unique owners, and allows you to track the quota usage for every "real" user. It also implements a "sub-admin", a partially restricted root user who has full read-only access to most subsystems, but write rights only to a limited subset, for example writing to files or killing processes only of certain users.
Nexenta is a complete GNU-based operating system built on top of the OpenSolaris kernel and runtime. The Debian system is used for software distribution and packaging to glue the numerous pieces together. However, Nexenta is not currently part of the Debian Project, nor are its packages present in the Debian database. It includes Apache, MySQL, Perl, Python, PHP, Firefox, Evolution, a software update manager, Synaptic package manager, Gaim, Abiword, administration and development utilities, editors, graphics, GNOME, interpreters, libraries, and much more.
OpenWrt is a Linux distribution for wireless routers. Instead of trying to cram every possible feature into one firmware, it provides only a minimal firmware with support for add-on packages. For users, this means the ability to custom-tune features, removing unwanted packages to make room for other packages. For developers, it means being able to focus on packages without having to test and release an entire firmware.
The MachOS project is a reference build of the original CMU Mach kernel distribution and documentation for development of new distributed computing platforms that require integrated IPC and multi-processor support. The project includes the kernel source distributions and a GNU based cross compile build chain.