Panda3d is a Python based Game Engine that is Open Source and Free. It is well documented and you can find most functions or properties in the docs.
Godot Game Engine offers common 3d functions and properties in a nice GUI.
Inkscape is software for making vector drawings and other technical drawings.
GIMP is an Open Source Raster Graphics Editing and Creation software.
Modeling and Animation
Structure Synth lets you code objects in an additive synthesis method, starting with basic shapes and functions that come together into more complex objects.
Structure Synth Website
Blender is software for 3d Modeling, Texturing, Rigging, Animation, Shaders, Compositing, Video Editting, and more!
FL Studio (Non-Free)
FL Studio is software for Writing, Composing, Sequencing, and Mixing music tracks.
FL Studio Website
OpenMPT is music tracker software, you can add samples, Compose, and Sequence patterns of Tracker music.
Alter-Ego is a program that allows you to take voice samples and write lyrics to be sung by that voice; Free Vocal Synthesizer.