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AtomTime98
AtomTime98 is a 32-bit Windows Internet (Winsock) application which will connect to the Atomic Clock time server in Boulder, Colorado (USA) and fetch the current atomic clock time value. It compares this value to your PC time and displays the difference. You then have the option of updating your PC clock to match the atomic clock value. There are a number of options to automate the update process. AtomTime98 also features support for most proxy servers.

Dimension4
Dimension 4 is the best time synchronization utility available today for Windows 95 and Windows NT 4.0.

Tardis
Tardis is a shareware utility for Windows that makes sure your PCs clock tells the right time. It can find out what the right time is in various ways including accessing Internet-based Atomic Clocks, using networked timeservers, GPS (The Global Positioning System), and by listening for time broadcasts over a LAN.

Vremya
Vremya is a scriptable NTP client for Macintosh. It allows you to set your clock using a NTP server by polling or receiving broadcasts. It requires Open Transport TCP/IP version 1.1 or better.

Tardis K9
K9 is a small shareware utility that is used to make sure that the clock on your PC is synchronised with the others on your LAN. It does this by listening for NTP time broadcasts on your LAN.

Timesync server
The Network Time Protocol (NTP) is used to synchronize the time of a computer client or server to another server or reference time source, such as a radio or satellite receiver or modem. It provides accuracies typically within a millisecond on LANs and up to a few tens of milliseconds on WANs relative to Coordinated Universal Time (UTC) via a Global Positioning Service (GPS) receiver, for example.