Cookie Caster - http://www.cookiecaster.com/
Lithophane - http://3dp.rocks/lithophane/
Instructables - http://instructables.com/
NASA 3D Resources - https://nasa3d.arc.nasa.gov/
3D Warehouse - https://3dwarehouse.sketchup.com/
Smithsonian - https://3d.si.edu/
ShareCG - http://www.sharecg.com/
All3DP - https://www.all3dp.com/
3DExport - https://de.3dexport.com/
3DContentCentral - https://www.3dcontentcentral.com/
3DShook - http://www.3dshook.com/
3DExport - https://de.3dexport.com/
3DContentCentral - https://www.3dcontentcentral.com/
Print a Brick (Legos) - https://printabrick.org
Repables - https://repables.com/
SketchFab - https://sketchfab.com/
Tinkercad - https://www.tinkercad.com/
Evermotion - https://evermotion.org/downloads/
Blendswap - https://www.blendswap.com/
3DModelfree - http://www.3dmodelfree.com/
Yobi3D - https://www.yobi3d.com/
ThreeDscans - http://threedscans.com/
BlankRepository - https://www.blankrepository.com/
3ddigitaldoubles - http://3ddigitaldoubles.com/
Pixellabs - https://www.thepixellab.net/freebies/