OneCalendar 5.6 for Mac could be downloaded from the developer's website when we last checked. We cannot confirm if there is a free download of this app available. We recommend checking the downloaded files with any free antivirus. This free Mac application was originally designed by Code Spark. The program is categorized as Productivity Tools.
From the developer:
OneCalendar lets you view in one window all your calendars, including Google calendar, Live/Outlook calendar, Exchange calendar and Facebook events. It integrates all your calendars into an easy-to-read overview. You can view and manage all your appointments, events and birthdays. You can easily filter the appointments you would like to see.
You may want to check out more Mac applications, such as GeburtstagsChecker, OmniGrowl or QuickNote, which might be related to OneCalendar.