Free, online advanced image and photo editor supports formats from Adobe Photoshop, GIMP, Sketch App, and more.
SculptGL
Shape a giant ball of digital clay with this web-based sculpting application. Find tutorials in the 'About & Help' section. Mr. DeVries says to focus on the Sculpting and Painting tools. Designs can be 3D printed.
TinkerCAD
Create 3D designs in a 3D printer friendly format. Click 'Learn' for tutorials. Sign in with your jefftwp Google account.
Makers Empire
"Stellar 3D design hub promotes innovation, collaboration, and creation" (Commonsense.org)
3D Slash
"Minecraft-like 3D modeling (and printing) made super easy for all ages" (Commonsense.org)
Autodesk Design Academy
"Outstanding project-based tutorials for popular engineering software" (Commonsense.org)