Various tools are useful when working with 3D prints, in order to design parts. The following are those which have been actively used in our team to produce parts. Many other options exist which are not listed here.
This is our primary design tool to design custom parts for both printing and machining.
OpenSCAD is a powerful tool which allows for mechanical parts to be described in a text language. The most common usage for our team is to download generators shared on Thingiverse for generating variations of common objects such as gears, pulleys, and hubs.
This is a tool owned by AutoDesk. It can be used to alter and combine STL files used for 3D prints.
The primary value of this tool is to correct defects in STL files obtained from public sources which will result in print defects. It is usually not needed for STL files we generate from Fusion 360.