Downloading Snap4Arduino 51.0 for Mac from the developer's website was possible when we last checked. We cannot confirm if there is a free download of this app available. The software lies within Developer Tools, more precisely Debugging Tools. The actual developer of this free Mac application is Edutec. 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.
From the developer:
Snap4Arduino is a modification of the Snap visual programming language that lets you seamlessly interact with almost all versions of the Arduino electronic prototyping board. In case it complains about a missing library, you can sudo run the postinstall.sh script, which will attempt to automatically take care of the issue.
You may want to check out more Mac applications, such as RIATest, ClippingDetector or Bugz, which might be similar to Snap4Arduino.