FitNesse. UserGuide.
TodaysDate [add child]
To diplay todays date:

Markup Text
Displayed as
Today is !today. Today is 04 Feb, 2012.
XML is !today -xml. XML is 2012-02-04T03:51:03.
Right now it is !today -t. Right now it is 04 Feb, 2012 03:51.
Tomorrow is !today +1. Tomorrow is 05 Feb, 2012.
Last week was !today -7. Last week was 28 Jan, 2012.
The month is !today (MMM). The month is Feb.

As you can see, you can add or subtract days. You can include the time tiwh -t. And you can use your own format for the time. (See SimpleDataFormat for the syntax.)