I use Thunderbird every day for my emails and calendars. I have to say I love it!
Here's what the Thunderbird team say about themselves
"Thunderbird is a free and open source email, newsfeed, chat, and calendaring client, that’s easy to set up and customise. One of the core principles of Thunderbird is the use and promotion of open standards - this focus is a rejection of our world of closed platforms and services that can’t communicate with each other. We want our users to have freedom and choice in how they communicate."