Proton Calendar is a privacy-focused calendar app from Proton AG (Geneva, Switzerland). It encrypts all event details end-to-end so that not even Proton can see them. Proton emphasizes Swiss jurisdiction: the company is headquartered in Switzerland, meaning user data is protected by strict Swiss laws. The calendar integrates with Proton Mail for secure invitations and offers features like scheduling, reminders, and shared team calendars. The site notes that over 100,000 businesses and 100 million users use Proton products. It does not list a founding year, but Proton was established in 2013.