daemontools is djb's framework for running "services", processes which need to always be running on the machine. Many of the other programs mentioned on this site can be set up to run under daemontools; this page is a set of links to the pages which contain that information.
It also has information about problems which you may encounter when setting up or running daemontools on your own system.
upstart is an "init" replacement system used by Fedora 9 and later, and optionally by several other Linux distributions. It works with the same "/etc/rcn.d" scripts that init uses, but it doesn't use the /etc/inittab file at all.
The daemontools install script looks for an "/etc/inittab" file, and if it finds it, adds a line to the end so that the normal system boot procedure will start svscan. upstart has this file, but doesn't use it. This means that daemontools does not start automatically when these systems boot up.
This page explains how to make it work.