Observation Manager 1.321 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.
According to the results of the Google Safe Browsing check, the developer's site is safe. Despite this, we recommend checking the downloaded files with any free antivirus software. The program lies within Education Tools, more precisely Science. This free Mac app is an intellectual property of Dirk Lehmann.
From the developer:
Observation Manager is a free and open logbook for (amateur-) astronomical observations. It's written in pure Java and runs on every platform supporting Java 1.4 or higher. All logbook entries made in Observation Manager are stored in the free and open OpenAstronomyLog XML Schema.
Log your observations and make sure next time you're searching for a celestial object you can take benefit of your past observations.
You may want to check out more Mac applications, such as Soccer Manager 2015, MeD's Movie Manager or Home Loan Manager Pro, which might be similar to Observation Manager.