AtomSync - A background utility that periodically checks a PCs clock against an internet NTP time server or against a computer in a LAN (local network) which runs an AtomSync LAN time server.
Beagle Software - Software and hardware to keep computer clock synchronized to the Atomic Clock over the Internet.
Chrony - A Unix-based NTP implementation specifically written to be suitable for computers with dial-up connections to the Internet.
FACTS - A freeware GUI-based SNTP client for the Amiga, which will synchronize system time to a server across the Internet. It is also capable of automatically switching in and out of DST.
Java Clock Applet - Supports network synchronization via SNTP, HTTP, Time, and Daytime protocols. Free download.
Sync-It with Atom - Network Time Protocol client for Windows with a nice user interface.
TymServ - Time reference that draws from multiple time sources. Computer networks and systems can be automatically synchronized.
WorldClock - Allows the user to synchronize his or her PC to Internet time servers. Supports both the Time or SNTP protocols. Also provides timezone, alarm and calendar features.