Sounds like a very silly question, but I tried, and it isn\'t too easy to find a simple answer to this simple question on google.
The longer story:
Before
SharePoint does support iCalanders. I am currently using on an events list so people can save to their outlook.
You can download the .ics based on the url like so:
http://yoursite/_vti_bin/owssvr.dll?CS=109&Cmd=Display&List=%7BListID%7D&CacheControl=1&ID=1&Using=event.ics
Replacing yoursite with your host name, ListID with the ID of your list with the events and the ID=1 with whatever list item number you want.
In SharePoint designer you can implement into the page as a hyperlink like the following example:
http://yoursite/Marketing/_vti_bin/owssvr.dll?CS=109&Cmd=Display&List=%7BA742AAC4%2D2654%2D4E64%2D9280%2D7813D2A343A2%7D&CacheControl=1&ID={$thisNode/@ID}&Using=event.ics
I'm not sure about a direct web service to retrieve the iCal if you want to use pragmatically but i'm sure you can just use this URL and a stream reader to save or manipulate.
Again, maybe not a very direct way of exporting to iCalendar, but this may help to get there anyway. I found on Sharepoint 2007 (and I am not sure whether 2010 has this feature, too, but it's quite possible), that you can create your own views of a calendar by using the "View" button and menu:
I found that MS Excel 2013 for some reason doesn't want to paste the contents of the clipboard thus obtained, but LibreOffice Calc does it just fine without any complaints. The specific calendar I exported in that way had some 1,300 events spread out over five years.
Single Calendar Event in iCalendar (iCal/CalDav) format
Open SharePoint calender event, click on the 'Custom Commands' tab and click 'Export Event'. You will be prompted to save a file of '.ics' type - this is the iCalendar compatible file and once opened will work with all calendar clients.
You can use the "RSS Feed" option in the "Calendar Tools" section to help find the correct url. Each item in the RSS feed will have an event.ics generated by the owssvr.dll, which you can then convert to the format described by kravitz88 to get an ics for the whole calendar.
If your original URL was something like this:
http://SHAREPOINT.local/siateam/Lists/Calendar/calendar.aspx
Then inside the RSS item links should look something like this:
http://SHAREPOINT.local/siateam/_vti_bin/owssvr.dll?CS=65001&Cmd=Display&CacheControl=1&List={df83eb1b-0403-42ec-8198-ec523bf1acc1}&ID=254&Using=%2Fsiateam%2FLists%2FCalendar/event.ics