Download of SketchChair 0.9.0.1 for Mac was available from the developer's website when we last checked. We cannot confirm if there is a free download of this app available. The application is included in Design & Photo Tools. We recommend checking the downloaded files with any free antivirus. This free Mac app is a product of Diatom Studio.
From the developer:
SketchChair is an open-source software tool that allows anyone to design and build their own digitally fabricated furniture easily. Within the program, you can upload chairs you have created, adding them to a growing collection of open-source designs in the SketchChair Design Library. Any of these chairs are freely available to be downloaded and edited by anybody, allowing chair designs to evolve as users continually refine and modify them.
You may want to check out more software for Mac, such as Realsoft3D, Argon v8 SP2 or FRS Coloring Book Volume 2, which might be related to SketchChair.