When a business needs a truly public calendar simply editable by all, it is not clear what best to do in Exchange or especially Exchange Online. Shared mailboxes and room calendars look like they should do it but don’t. One way is to create an ordinary user mailbox and then give all users full delegation rights in Powershell:
Get-Mailbox | foreach-object { Add-MailboxPermission -Identity "Public Calendar" -User $_.SamAcc
ountName -AccessRights FullAccess }
The only catch is that this does require a license.