Download of WallCal 1.7.1 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 application lies within Productivity Tools, more precisely Mind-mapping. The actual developer of this free software for Mac is tsukie. We recommend checking the downloaded files with any free antivirus.
From the developer:
WallCal puts a semi-transparent background calendar right on desktop wallpaper. A keystroke or mouse click can bring it to the front most, and with another keystroke or click it will return to the background. You can instantly see and recall what your calendar/agenda/todo-list currently is as soon as you go back to the desktop wallpaper.
You may want to check out more software for Mac, such as WallCal Lite, which might be similar to WallCal.