DevIcon 3.0 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. 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. This free software for Mac OS X is a product of Softlibs.
From the developer:
DevIcon is a simple application that helps developers generate @1x, @2x, and @3x icons quickly. The results can be exported as iPhone、iPad、and Mac application icons. The icons can be easily adjusted in terms of width and height. They can be saved at a computer location of your choice.