OddCal 2.1.2 for Mac was available to download from the developer's website when we last checked. We cannot confirm if there is a free download of this app available. The actual developer of this software for Mac is Craig Smith. Please check the Mac app with an antivirus before launch as it is downloaded from the developer's website, and we cannot ensure that it is safe. The application lies within Lifestyle Tools, more precisely Bookkeeping & Cataloging.
From the developer:
This application helps you enter multiple events into your Calendar that don't have a repeatable pattern. You can choose as many dates as you like, and assign the same Event Title (with or without a Location, Alarm, or a Note) to all of them. Events can have the start and end points, or be marked as all-day.
You may want to check out more software for Mac, such as BookTracker, Reunion or HanDBase Desktop, which might be similar to OddCal.