ntpd

xntpd is the Network Time Protocol version three (1992) daemon software.

The "x" was added to the name because the branch of code that eventually became NTPv3 was "experimental".

The name of the software changed back to "ntpd" for version four[when?]

because the inventor of NTP, Dave Mills, decided that something probably should not remain "experimental" for about twenty years in the absence of dramatic change.

ntpd uses a single configuration-file to run the daemon in server and/or client modes.