Calendar Utility
A Calendar utility on an intranet can be helpful for communicating holidays, significant corporate events and other general reminders (tax filing dates, etc.) to staff. This would appear universally for all intranet users on a Calendar page, or as a secondary item on a main page.
Calendars can be a real killer application in settings where people are often in and out of the office, as it increases the possibility of face-to-face communication among staff. The drawback of this, like many other tools, is that it will only be as valuable as its data's integrity. If people don't keep their schedules up-to-date and/or its adoption rate isn't very high, then the data will be unreliable and the components chance at success will suffer.