Move your mouse over Settings and click on iCalendar.
Click on the corresponding button, select to save the file to your computer.
Any calendar software (mac, pc, linux) should be compatible, access its software support to find out more. Some examples of how to load the download files into various applications are given below;
Thunderbird (Lightning): On the File menu while viewing you Lightning calendar select Import Calendar
Outlook 2003 & 2007: On the File menu, choose Import and Export. Under Choose an action to perform: select Import an iCalendar or vCalendar file (.vcs). See Microsoft support for more information.