Brickstructions 1.1 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.
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. The actual developer of this free software for Mac is Simone Civetta. The application lies within Games, more precisely Tools.
From the developer:
Brickstructions allows you to build and download LEGO instructions from some well-renowned community websites, such as Peeron, LetsBuildItAgain, and BricksArgz.net. You just need to type in the number of your favorite set and wait for Brickstructions to look for and download all the instruction pages. Brickstructions automatically creates PDF documents containing all the pages you need, with an optimal quality.
You may want to check out more software for Mac, such as GooTool, Mansion Level Builder or O2Em, which might be similar to Brickstructions.