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, PianoRoll or dvcUniversity, which might be related to Thortspace.