Download of Apertium 3.1 for Mac was on the developer's website when we last checked. We cannot confirm if there is a free download of this app available. The software lies within System Tools, more precisely System Optimization. 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 Mac app is an intellectual property of Apertium Team.
From the developer:
Apertium is a toolbox designed to help you build open-source shallow-transfer machine translation systems, especially suitable for related language pairs. The application includes the engine, maintenance tools, and open linguistic data for several language pairs.
You may want to check out more software for Mac, such as Dock Delight, Snow Checker or SBSystemPrefs, which might be similar to Apertium.