iCalCord is a Discord bot that generates iCalendar (.ics) feeds for Discord server events. It allows users to subscribe to their server's event calendar using any calendar application that supports the iCalendar format.
If you use Google Calendar, follow this guide to subscribe to the feed, then open Sync Settings and check the box for the calendar you just subscribed to, to make it propagate to non-Google apps. Google syncs ICS feeds every 12-24 hours, and that is not adjustable.
If you're using Google Calendar app on Android, you need to open Settings, select the newly added feed on the list and enable "Sync".
If you're using iCloud Calendar, "Add Subscription Calendar" option is only available in 1st party Apple apps. Once added in e.g. iOS app, subscriptions will propagate to 3rd party apps like Flexibits Fantastical and Mozilla Thunderbird. Subscription calendar feature is completely absent from iCloud.com web version though.
If the server is not "Discoverable", you have two options: