AppIcon 4.0 for Mac could be downloaded from the developer's website when we last checked. We cannot confirm if there is a free download of this app available. This Mac app was originally designed by Isaiah.v.Hunen.
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 program was developed to work on Mac OS X 10.6 or later. The most popular versions among the program users are 1.3 and 1.2. The software lies within Theming Tools, more precisely Icons & cursors.
From the developer:
​AppIcon is a free software program for the Mac* that can get an icon from every app. After getting it, you can edit it, as long it keeps the same size and extention. Then, you can upload it to the same app, or another! If you afterwards don't like it, don't worry, there is a icon-recovering feature included.
Note: You can't change the Finder Icon
You may want to check out more Mac applications, such as AppIcon Generator, Free AppIcon Generator or AppIcon Maker, which might be similar to AppIcon.