The 2.5 version of ACalendar for Mac was available to download on the developer's website when we last checked. We cannot confirm if there is a free download of this app available. The application lies within Lifestyle Tools, more precisely Bookkeeping & Cataloging. This software for Mac OS X is an intellectual property of Adriano Martins.
From the developer:
ACalendar is a simple calendar app which enables access to a month-to-month calendar directly in menu bar. With a modern layout, ACalendar enables you to: Select periods on each month aiming to temporarily underline critical occasions in each calendar view. Select different themes for the calendar. Display the date and time in Menu Bar instead of the application icon.
You may want to check out more Mac applications, such as BookTracker, Reunion or HanDBase Desktop, which might be related to ACalendar.