rdate is very nice. It keeps my computers on time.
Computers have a clock, but it isn't accurate. Far from it. People often wonder why computer clocks are so inaccurate - the answer is, they aren't clocks, they're computers. It would cost nearly $0.01 to make computers have accurate clocks, so it isn't going to happen.
But when you have a network, it's good to have all your computers have the same time. This is because some things need to happen after other things, and if they're on different computers, you need the clocks to be together.
Enter rdate. Once per day, I run "rdate -s tick.greyware.com" on my computer named xanth, and once per day, I run "rdate -s xanth" no all the other computers. rdate gets the time from port 37, on a service called "time-stream", which is built in to xinetd, the super-server, which I install by default on all my servers.
This works well. But it might not work in future. rdate has become "deprecated", and is on the way to being obsolete. That's a shame, because it means that one day I might have to change everything.
There's ntpdate that replaces it, which is a client to ntp (network time protocol). That's altogether more sophisticated and much more clever, and can syncronise much better than the "within a second or so" that rdate does. But the rdate sync is good enough for me. I hope I can continue to use it in future, because changing everything over to use ntp will be a bit of a pain.