TimeTree offers two sharing options.
One is a shared "Calendar" that share whole calendar,the other is a shared "Event" that share one-time event.
Note: the way of creating between a shared Calendar and a shared Event is different.
Convenient for sharing multiple events with different groups such as family, friends, coworkers, etc.
To create a shared calendar, invite members on Calendar More tab. (No an account registration required)
Convenient for sharing one-time event such as a party. An event host can select one group at a time and can be changed per event.
To create a shared event, invite members from Friends tab (An account registration should be required.)
-Friends List for Shared Events
This allows you to create a list and add members whom you often share events with