Assets
De todo - http://kenney.nl/
De todo - http://opengameart.org (modelos en el formato de blender)
De todo - Unity Asset Store - https://assetstore.unity.com/ (compatible con otros engine, no solo unity)
De todo - https://search.creativecommons.org/
De todo - https://archive.org
Paquete de modelos y sprites libres - https://itch.io/jam/asset-pack-jam/entries
Armas sprites 2d - https://kaylousberg.itch.io/gun-assets
Modelos 3D
3D models - http://turboSquid.com
3D models - http://www.blendswap.com/
3D models - http://www.sketchfab.com
Very high quality assets - http://devassets.com
Plenty of lowpoly models - https://poly.google.com/
Thingiverse (convert STL to OBJ using Blender) - https://www.thingiverse.com/
Texturas / Arte 2D
Texturas - http://www.cgtextures.com
2D sprites and Flash backgrounds (.fla) - http://glitchthegame.com/
Texturas (Parcialmente gratuito)- http://www.openfootage.net
Textures with PBR maps - https://3dtextures.me/
Audio
Music - http://www.newgrounds.com/audio
Music - https://expsyle.bandcamp.com/
Music - http://dig.ccmixter.org/
Music production - https://www.audiotool.com/
Music production - https://www.soundtrap.com/
Music production (Chip tunes) - http://sfbgames.com/chiptone/
Sound Effects - http://freesfx.co.uk
Sound Effects - http://soundbible.com
Sound Effects - http://freesound.org/
Sound Effects - http://99sounds.org/free-sound-effects/
Sound Effects - https://sonniss.com/gameaudiogdc2017/
Sound Effects - https://sonniss.com/gameaudiogdc2016/
Sound Effects - http://ftpmirror.your.org/pub/misc/sonniss/
Sound Effects - http://wiki.laptop.org/go/Free_sound_samples
Audition SFX - https://offers.adobe.com
Music (and graph paper!!) - http://incompetech.com
Text-To-Speech (Texto que habla) - https://soundoftext.com/
Free Music Archive (Libreria de musica de libre uso) - http://freemusicarchive.org/ (Podes buscar Musica libre de derechos usando los filtros en soundcloud y youtube)
Fuentes
Fonts - http://www.fontsquirrel.com
Google Fonts - http://www.google.com/fonts
Fonts - http://www.1001freefonts.com
Fonts - http://www.fontriver.com
Fonts - http://www.1001fonts.com
Da Font - http://dafont.com/FontStruct (Font Maker + Font Library) - https://fontstruct.com/
Carnegie-Mellon Motion Capture Database - http://mocap.cs.cmu.edu