openntpd - Free, easy to use implementation of the Network Time Protocol

NTP, the Network Time Protocol, is used to keep the computer clocks synchronized. It provides the ability to sync the local clock to remote NTP servers and can act as NTP server itself, redistributing the local clock.
This is an alternative implementation of the NTP software, made by the OpenBSD Project. It makes use of privilege separation, only implements a subset of the NTP protocol, adjusting the rate of the clock to synchronize the local clock.
Alternative packages which provide similar functionality are ntp and chrony.