Signup Sheet is a solution for when you have pre-committed times at which you'll hold an event, such that your calendar availability doesn't actually influence these predefined times. The primary goal of a signup sheet is to keep track of which guest reserves which spot. Each time (spot) can accommodate one or more guests, up to a max capacity that you define.
FreeBusy creates HOLD events on your calendar so you can keep track of the times you've offered, as well as which guests signed up for that time, which you can see in Agenda page. Guests receive an email confirmation from where they can add the event to their calendar. They do not receive a typical calendar invite.
How Signup Sheet works:
multiple participants can reserve a slot at the same time, depending on the setting above
calendar invites would not be sent to people who reserves a slot
times are fixed and cannot be rescheduled
actual calendar availability of organizer doesn't matter
HOLD events in organizer's calendar would be created for all time slots
new slots can be added later
FreeBusy uses your calendar as a storage for available times specified in signup sheet, to help tracking all participants and all predefined times that have a reservation using that link near other events in your calendar.
Specific Times is a solution for when you want to specify your availability for meeting with very fine granularity. As with other meetings, your calendar availability is taken into account and calendar invites are being sent to guests when people actually book a time with you.
How Specific Times works:
only single participant could reserves a slot
calendar invites would be sent to people who reserves a slot
actual calendar availability of organizer taken into account
Now it is in page. You can select an event type and find all relevant info about it there (in addition to your calendar).
To summarize:
