OpenNTPD is a FREE, easy to use implementation of the Network Time 
Protocol. It provides the ability to sync the local clock to remote 
NTP servers and can act as NTP server itself, redistributing the 
local clock.  OpenNTPD is primarily developed by Henning Brauer as 
part of the OpenBSD Project. The portable version is made by Darren 
Tucker. 

You will need to add the "_ntp" user and group to /etc/passwd and 
/etc/group if it's not present on your system.  Without these groups,
the package will not work.

You will also need to call the /etc/rc.d/rc.ntpd script from one of 
your startup scripts if you want OpenNTPD to start at boot; one way
is to add something like this to /etc/rc.d/rc.local:
  if [ -x /etc/rc.d/rc.ntpd ]; then
    /etc/rc.d/rc.ntpd start
  fi