s6 is a complete process supervision suite in the style of daemontools, runit, and perp. It provides a candidate for process 1. It also comes with a library and command line utilities that implement inter-process notification and synchronization.
finit is an extremely fast /sbin/init replacement with a focus on small embedded GNU/Linux systems. It is based on Claudio Matsuoka's original finit with I/O, service, and hook plugin extensions.