In addition to syncing with iCloud, BusyCal can also sync with other CalDAV Servers including Lion iCal Server and Snow Leopard iCal Server. It may also work with other third-party CalDAV Servers (Kerio, Zimbra, Communigate and Oracle Beehive) but has only been tested with Apple's iCal Server.
Select Connect to iCloud/CalDAV Server from the Calendar menu.
Select CalDAV from the popup menu and enter your Login, Password and Server address. The server address for most CalDAV servers is the server's fully qualified domain name, e.g. "caldavserver.fredco.com". Some CalDAV servers are running in non-standard configurations and require a fully qualified path to your calendar, e.g. "https://caldavserver.fredco.com:8443/CalDAV/calendars/". Your IT administrator or provider should be able to help you with this information.
The CalDAV server and its calendars will appear in the source list and begin syncing. You may now edit events on those calendars and the changes will be synchronized with the server.
Once you are connected to a CalDAV server, you can alter the server settings by control-clicking the server and choosing Server Settings. You may change your username, password, server address, and refresh interval. Push will be enabled by default, if the server supports it.
To remove a server, click the Disconnect button. Any calendars you are subscribed to will be removed from BusyCal, but the calendars will remain intact on the server.