Blender
Official screenshots
A mature cross-platform suite for characters, environments, animation, materials, and promotional renders, with common engine handoff formats such as glTF and FBX.
Why it’s here
A solo developer can cover most of a 3D content pipeline in one free tool, backed by an exceptional tutorial and add-on ecosystem.
Best fit
Art, animation, audio, levels, and narrative turn mechanics into a believable world.
Before you commit
Its breadth creates a substantial learning curve, and round-tripping proprietary formats such as FBX still needs validation in the target engine.