GroupCal is described as 'redefines the way calendars work. It introduces a whole new way to create and manage shared calendars between groups of people. Each shared calendar holds events for a specific topic, such as - family, friends, and co-workers' and is an app in the Office & Productivity category. There are more than 25 alternatives to GroupCal for a variety of platforms, including Mac, iPhone, Windows, Linux and iPad. The best alternative is Lightning Calendar, which is both free and Open Source. Other great apps like GroupCal are Rainlendar (Freemium), Apple Calendar (Free), Itsycal (Free, Open Source) and Kontact (Free, Open Source).
Fantastical 2 includes powerful features such as an incredibly intuitive parsing engine, a full calendar window (with day, week, month, and year views), a quick access mini window, iCloud reminders support, time zone support, and much, much more.
Kalendar is a Kirigami-based calendar application that uses Akonadi. It lets you add, edit and delete events from local and remote accounts of your choice, while keeping changes syncronised across your Plasma desktop or phone.
Dato is a replacement for the system menu bar clock. By default, it looks exactly the same, but when you click it, you get a small calendar, calendar events, the current time in various time zones, and more.
See your calendar events quickly and easily at a glance, without opening the calendar application. Pixel scheduler places a bar on your screen, with your events displayed as ‘blocks’. Just look to the bar to see your events, and hover for details.
Maya is a slim, lightweight, GCal-syncing GTK+ Calendar application written in Vala, specifically for elementary OS . Also looks and works great on other GTK+ desktops. In elementary OS, Maya is known as Calendar.