What are some alternatives?
When comparing Ops Calender and Apple Mail, you can also consider the following products
Teamup Calendar - Cloud-based calendaring using capability URL, application developed in Zurich, Switzerland.
Thunderbird - Thunderbird is a free email application that's easy to set up and customize - and it's loaded with great features!
Teamweek - A project management software to help you get the best overview. Plan fast, change plans faster!
Outlook - Organize your world. Outlook’s email and calendar tools help you communicate, stay on top of what matters, and get things done.
Time.ly - Time.ly is a collaborative calendar solution for websites.
eM Client - eM Client is a Windows-based email client for sending and receiving emails, and managing calendars, contacts and tasks.