Tardis is a shareware utility for Windows that makes sure your PC�¯�¿�½s 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), Radio clocks, and by listening for time broadcasts over a LAN. The Service version of Tardis 2000 runs as a Windows NT/2000/XP "service", just like other services that come as standard with Windows.
If you want your clock to be correct ALL THE TIME, this is the program for you.
Great software
Pros
Reliable, can skew clock rather than simply stepping the time, can log to event log, can run as service.
Cons
It could be a little easier to manage the time servers. If you have a large list and wish to move a particular server, for example, you will find yourself right clicking and selecting "Move Up" or "Move Down" many times over.
Summary
Very reliable, good features, good support. This was designed for serious real-world use, not to make a quick buck.