Hotplug2 is aimed at early Linux user space, i.e. initramfs or initrd, and possibly also at embedded devices (such as WRT-like routers) or very weak machines, such as 386/486. It connects to the uevent netlink socket and reads events. The application generally operates in two modes: dumb and smart.
Cobbler is a network installation and update server. It can be used to automatically set up PXE, install virtual guests, manage answer files, and reinstall existing Linux machines. Advanced features include importing distributions from DVDs and rsync mirrors, kickstart templating, integrated yum mirroring (integrated with the installer to make updates available at install time), creation of netboot ISOs, and built-in DHCP/DNS Management. Tools such as "cobbler triggers", a Python API, and an XMLRPC API allow integration with cobbler with the rest of your datacenter environment or other systems management applications. There is also a Web interface to simplify management of the install server. Cobbler supports RHEL 4+, Fedora, and derivative distributions, and is also able to install other popular distributions.
btfs can be used as /init for constructing a run-time environment before running the real init. It supports extracting compressed (*.cgz, *.cbz2) and uncompressed (*.co) cpios located on a compile-defined directory (/). Also, it creates a tmpfs filesystem as the new root, if / isn't one already and the purpose of the initramfs isn't for starting a system in another location (disk, network, etc.). That will allow for the data on / to be swapped to disk when swap devices are activated later.