Steve Litt:
...
> * Runit
> * S6
...

Why not busybox init, it handles gettys and the rest is up to
/etc/rcS, which you are free to make it do whatever you like.

As a direct replacement for sysv init, you can use
for i in /etc/rcS.d/S* /etc/rc2.d/S*
do
$i start
done

in rcS and similar for shutdown.

Regards,
/Karl Hammar