Download of DataNucleus 5.2.1 for Mac was available from the developer's website when we last checked. We cannot confirm if there is a free download of this app available. The program lies within Developer Tools, more precisely Webmaster Tools.
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. This free software for Mac OS X is an intellectual property of DataNucleus Team.
From the developer:
DataNucleus provides Java data persistence to a range of datastores using JDO/JPA/REST APIs. The program enables users to better manage the application data in a Java development environment. You can use a single common interface for all of your data.
You may want to check out more software for Mac, such as Browsealoud, RAGE WebDesign or solr, which might be similar to DataNucleus.