Winat is a GUI frontend for Windows NT's schedule service, which handles automating jobs (comparable to cron for unix). It makes scheduling jobs a bit easier, since you just type in what you want to happen and when. Whereas with only schedule you use the "at" command to submit jobs to the schedule service. And since schedule is indeed a service, the machine (usually) doesn't need to have a user logged in to perform the job.

Like Bitsurfer said, it's in the NT Resource Kit.

While it is a bit simpler then just AT, make sure to test your jobs. Various jobs I've Winat'd have gone awry, or not gone at all. There are better and newer equivelents of this program, most of which are free.