jailinit serves as a replacement for FreeBSD's init(8). It is intended for use with virtual servers started by a jail(2) system call and more specifically the jail(8) userland tool in FreeBSD. If you use jail(8) to launch a virtual server, the application you should launch within the jailed hierarchy is /sbin/init, which should be replaced with jailinit.  

This init replacement will function as you might expect. It will bring the system into a multi-user state and handle /etc/rc for runtime configurations as usual. This init replacement will accept signals from outside or inside the jail for the purpose of restarting or stopping the virtual server.

See also: http://www.freebsd.org/doc/handbook/jails-build.html

The last time I tested this was with FreeBSD 4.0-STABLE - quite some time ago. There may be more appropriate solutions available now.