I am looking to add functionality to my website where users can add an event to their calendar. This has raised the issue of compatibility, as there are a lot of potential calendar options that end-users could be using (Outlook, Google, iCal to name a few). Making the issue even muddier is that calendars can be either local software and online cloud service.
Is there a universal or cross-platform specification I can use to publish calendar events, or am I stuck writing to several different specs and making the user choose which one they need to download?
You're probably looking for the iCalendar format.
iCalendar is used and supported by a large number of products, including Google Calendar, Apple iCal, GoDaddy Online Group Calendar, IBM Lotus Notes, Yahoo! Calendar, Evolution (software), Lightning extension for Mozilla Thunderbird and SeaMonkey, and partially by Microsoft Outlook.