On Multiply you can keep track of all of your personal events, as well as view an aggregated version called the network calendar that includes all of your contacts' events as well.

In your personal calendar, you can use the same privacy settings that are available in all posts on Multiply. So you may choose to set "Twelfth Night - Opening Day" to "everyone" but save something like "Hernia Operation" to only "contacts" and perhaps save "Get Hair Cut" in a post that's a handy reminder just for you.

The network calendar includes not only your posts, but posts by your contacts as well (if they've set the privacy settings such that you can see them). You can also customize your network calendar. By clicking on the "view calendar" link on my messages page, you can set your calendar to show you just your contacts events, or extend that to your wider network. You can also include group events if you'd like.