Tinkercad is a free CAD package, which you may conveniently access via a Polar Cloud link; see Section 6.3.1. You must create a Tinkercad account in order to use Tinkercad, but such an account is free and easy to create.
Tinkercad supports direct export of its objects to the Polar Cloud; see Section 6.3.2.
As with any CAD package supporting industry-standard .stl files, you may also import Polar Cloud objects into Tinkercad, to edit or manipulate them using Tinkercad; see Section 6.3.3.