Ficl (Forth inspired command language) is an ANS Forth interpreter written in C. Unlike traditional Forths, this interpreter is designed to be embedded into other systems as a command/macro/development prototype language. Ficl provides object extensions that can be used to wrap methods and structures of the host system without altering them.
Hotplug lets you plug in new devices and use them immediately. That means that users won't need to learn so much system administration, since the Linux system will at least partially autoconfigure itself. Initially, hotplug included support for USB and PCI (Cardbus) devices, and could automatically configure some common network interfaces. Updated versions include IEEE 1394 (Firewire/i.Link) support and can download firmware to USB devices that need it.
The Linux Bootdisk HOWTO describes how to design and build boot/root diskettes for Linux on the Intel platform. These disks can be used as rescue disks or to test new system components. You should be reasonably familiar with system administration tasks before attempting to build a bootdisk.
DOCSIS Server is a DHCP/TFTP/TOD/syslog server that uses MySQL as a backend. If you have a DOCSIS Cable Modem headend, you can use this server to boot up cable modems and assign IP addresses to customer premise equipment. With a little bit of tweaking you could also use it as just a DHCP server attached to a MySQL database. It was designed to boot up more than 150 modems per second.
eINIT is an alternative init system. It's quite fast, since it can potentially be used without the help of any scripting at all, but it is still flexible and extremely modular. The focus is on speed and parallelisation, mostly with embedded devices and low-downtime servers in mind, and benchmarks do suggest that it's doing a fairly good job at that. It compiles cleanly (and should thus work, provided someone writes appropriate modules) on Linux, FreeBSD, and Darwin/Mac OS X.
Debian From Scratch is really two related components in one. First, it's a live bootable CD image that is designed to provide a full-featured kernel and rescue environment. It includes filesystem tools, editors, C compilers, Python, Perl, and everything you need to manually install Debian on a new machine. On ix86 machines, Grub is used to boot directly from the CD. There is also a program that is used to create the DFS CD images. It is highly configurable and can be used to create other custom bootable CD or DVD images. You can include whatever kernel or packages you want.