Cross-platform calendars

Hi everyone!

I couldn't find this through a search, so I'm creating a thread on it. Let's talk about calendars for a cross-platform user - what do you use and how do you sync?

I've always only used iCal on my iPhone and Mac and synced through my Apple ID, but this won't work with my Linux gaming rig. I want to use it for work too, so I need to be able to

- create new items on any device and

- sync them across all devices!

Google Calendar has native apps for all three platforms but... it's Google and I'd prefer to avoid their apps and syncing over my G account. How do you calendar?