Download of Thortspace 1.6.6 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. Thortspace for Mac lies within Education Tools, more precisely Teaching Tools. We recommend checking the downloaded files with any free antivirus.
From the developer:
3D visual thinking for creative brainstorming, problem solving, collaborative research and education. Beyond 3D mind mapping – reflecting how minds work.
You may want to check out more software for Mac, such as Dolce Music Flash Cards, dvcUniversity or FRS Money Math, which might be related to Thortspace.