Vdirsyncer is a command-line tool for synchronizing calendars and addressbooks
between a variety of servers and the local filesystem. The most popular usecase
is to synchronize a server with a local folder and use a set of other programs
to change the local events and contacts. Vdirsyncer can then synchronize those
changes back to the server.

However, vdirsyncer is not limited to synchronizing between clients and servers.
It can also be used to synchronize calendars and/or addressbooks between two
servers directly.

It aims to be for calendars and contacts what OfflineIMAP is for emails.