I had a play around on Google Calendar. I can see why it is popular, as I found it very straight-forward to use. A benefit, too, is that it can be accessed from anywhere so long as you have an Internet connection, and you can share it with others.
We used something very similar at my previous library (I can’t remember which application off the top of my head), which was so, so useful. Being able to see when others were away on annual leave, or out for a meeting, meant less time running around the library trying to find them to answer a phone call, when they’re potentially not even around! It was also used to arrange the desk rota, which was helpful as it was built around your schedule, rather than the other way around.
A calendar like this is definitely something I would consider introducing if my organisation didn’t already use it.
However, I won’t be using it for myself, as I already have a trusted system; two calendars and a diary!