It’s only for messages. No calendar migration
Imapsync command is a tool allowing incremental and recursive imap transfers from one mailbox to another. If you don’t understand the previous sentence, it’s normal, it’s pedantic computer-oriented jargon.
All folders are transferred, recursively, meaning the whole folder hierarchy is taken, all messages in them, and all message flags (\Seen\Answered \Flagged etc.) are synced too.
Imapsync reduces the amount of data transferred by not transferring a given message if it already resides on the destination side. Messages that are on the destination side but not on the source side stay as they are.
Get the tool here https://github.com/imapsync/imapsync