Even tho generally it saves litte power for making noticeable lag when starting CPU-intensive tasks (as CPU has to upclock beforehand), sometimes we only care for every single saved watt (Like in case of laptops and other battery-run stuff) and don't give a crap 'bout performance anyway. That's where estd comes in.

estd(1) is not included in base, but can be easily obtained from pkgsrc:

# cd /usr/pkgsrc/sysutils/estd
# make install

Or, if ye got pkgin(1) on system:

# pkgin in estd

estd works OOTB (Out Of The Box), that means ye don't get to configure it, so it's just nothing but copying rc file to /etc/rc.d and setting estd=YES in /etc/rc.conf, in order to enable it at boot time:

# cp -p /usr/pkg/share/examples/rc.d/estd /etc/rc.d/
# echo estd="YES" >> /etc/rc.conf <-- Do not mistype ">>" as ">"!
# service estd start

[1] (N) following program name means section of it's manual page. In this case it's section one (General commands). It's useful when there are several manpages named the same but under different sections, so you can for example write "man 5 postconf" to make sure you get a manual page about postfix configuration options, not postconf(1) configuration utility