Openntpd

From AdminWiki

OpenNTPd is OpenBSD's ntpd.

It's designed to be secure, easy to set up and run smoothly. Of course it can also act as a full featured NTP server and export the local time.

On old Linux machines, openntpd comes in very handy, if your old ntpd won't talk to your fresh NTP Servers. Just fetch the "Portable" version from http://www.openntpd.org/portable.html and "make install" it.