I don't think I have to explain what calendar rules my working day - google calendar obiously. My email is google hosted (google's fabulous domain apps) and so on. But how about other apps ? A few weeks back, everybody was talking about twitter. Would that be useful within an office ? The answer is yes. How ?
Using twitter is a perfect way of seeing and monitoring development of coworkers or project team members - you can easily follow eachother. Perfect for virtual teambuilding ! Besides that you could probably use it as a news source.
What online tools is used in your company ?