Source Ruckus Linux is an embeddable, robust Linux meta-distribution. It's a collection of build tools, source packages, scripts, and documentation all ready to be built into a Linux distribution. It can be used out-of-the-box, but its real strength lies in being used as a base for your own distribution. In other words, it exists purely to be forked, although it can be used as-is.
RuckusRD is a drop-in replacement for mkinitrd that's intended for use on embedded systems or removable media (e.g. live CDs), but is also perfectly usable on normal desktop Linux systems. Its main strength is its non-memory-retentive read-write root filesystem support, which combines a read-only SquashFS image with a RAM overlay. This utility is part of the Source Ruckus project.
confinedrv creates a new device node /sdx under /dev/mapper which mirrors the given base drive with certain partitions faded out and other partitions limited to read-only or read-write access. It is commonly used to safely boot an existing OS installation with Qemu or any other virtualization software from the same hard disk as the host operating system has been booted from.
VyOS is a Linux distribution for routers and firewalls which features a unified commandline interface and a single configuration file, with an API for extending it. It includes BGP, OSPF, and RIP routing protocols, policy-based routing, a DHCP and caching DNS server, a Web proxy, and more. It runs on x86 physical machines and a variety of hypervisors, including KVM, Xen, VMWare, and Hyper-V. VyOS is forked from Vyatta and based on VC6.6 source code.