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.
mbootpack is a tool that takes a Multiboot kernel and modules (e.g. a Xen VMM or a xen-linux kernel and initrd), and packages them up as a single file that looks like a bzImage Linux kernel. The aim is to allow you to boot Multiboot kernels (specifically, Xen) using bootloaders that don't support the Multiboot standard (i.e. pretty much anything except GRUB).
Partition Logic is a partitioning and disk management tool for PC-compatible computers. It includes its own standalone operating system and GUI, and can fit on a single bootable floppy (or CD). It creates, modifies, resizes, deletes, formats, and moves partitions, and copies hard disks. It is based on the Visopsys operating system.
Matjito is a pluggable library for the rapid computation of mathematical expressions in C++ programs. Its accepts either an expression string with information about the mapping of symbols to variables and functions or an n-ary tree representing the expression. It features an x86 JIT that allows expressions to be computed very quickly, and is comparable or even better than code generated by optimizing C compilers. It can be used on non-x86 CPUs in a slower interpreting mode.
Necromancer's Dos Navigator is a "Norton Commander" clone. It uses a well known text-mode interface, is highly customizable, and has a lot of features. Its key features are a text editor with syntax highlighting, horizontal/vertical blocks, multiple codepages, undo/redo, bookmarks, powerful searching, and regex; a file viewer with text view, asm/dump/hex edit, raw blocks, header viewer, search, regex, and unlimited filesize; a powerful filepanel with higlighting, VFSs, and filefind with textsearch and regex; a calculator; and more.
Kerrighed is a Single System Image operating system (SSI) for clusters. It offers the view of a unique SMP machine on top of a cluster of standard PCs. The goals are high performance of applications, high availability of the cluster, efficient resource management, high customizability of the operating system, and ease of use. It is implemented as an extension to Linux operating system (a set of Linux modules and a small patch to the kernel).