Udev, a collection of tools and a daemon to manage events received from the kernel and deal with them in user-space, has been merged with systemd.
Kay Sievers, the lead developer for Udev, has explained that the Udev packages will still be installable independently.
“This option will be supported in the long term because separate builds are required to ensure that initrds (initial ramdisks), which don't include systemd, work correctly. Distributions that don't use systemd can continue to build udev as before, but will have to use the systemd source”, said Sievers.
The reason for this decision is pretty clear-cut, at least according to the developers, a modern init system must be fully hotplug-capable and the udev device management and knowledge about device lifecycles is an integral part of systemd and not an isolated logic.
systemd is a system and service manager for Linux, compatible with SysV and LSB init scripts.