RunAsDate is a small utility that allows you to run a program in the date and time that you specify. This utility doesn't change the current system date and time of your computer, but it only injects the date/time that you specify into the desired application.
You can run multiple applications simultaneously, each application works with different date and time, while the real date/time of your system continues to run normally.

www.nirsoft.net/utils/run_as_date.html

I think this smiler to MS Schedule Task

It's bit different. MS Scheduled Task is used to run an application in a scheduled date and time which happens to be in future.

But RunAsDate is used to run a application, while changing the current time as users requirement. As an example think of a software that came up with 30days trial. Once trial has been expired you can simply run the same application emulating as you are running it on the day you installed the software. (Actually, this is not true for all trial wares, because it is possible to avoid such bypasses) So this software is basically used to run an application forcing it to believe it is running on a date in past or future.