Asset Libraries
itch.io Game Assets — Largest free game asset marketplace. Thousands of sprite sheets, tilesets, character packs. Many CC0 licensed.
Kenney.nl — Over 40,000 free game assets: 2D sprites, 3D models, UI elements, sound effects. All CC0 public domain. The gold standard for prototyping.
For more on this topic, see our guide on how to publish your first game on steam: complete guide.OpenGameArt.org — Community-driven library of 2D/3D art, music, and sound effects. Multiple license types, always check before commercial use.
Sound & Music
Freesound.org — 500K+ sound effects, CC licensed. Essential for SFX. Incompetech — Kevin MacLeod royalty-free music (CC-BY). Mixkit — High-quality free music and SFX, no attribution needed.
UI Kits
Kenney UI Pack (free), Fantasy UI Kit on itch.io, Google Material Icons for modern interfaces.