Depends entirely on what you're looking for. Tell me:
| Category | Sites |
|---|---|
| Browser free | CrazyGames, Poki, Kongregate, Armor Games, Newgrounds, itch.io (web), Miniclip |
| Indie downloads | itch.io, Game Jolt, Steam (free filter), Epic (free weekly), GOG |
| Retro/Emulation | Internet Archive (Console Living Room), My Abandonware, DOS Games Archive |
| Mobile | App Store, Google Play, TapTap, F-Droid (open source) |
| PC Storefronts | Steam, Epic, GOG, Humble Bundle, Fanatical, Green Man Gaming |
| Learning/Edu | Khan Academy, Brilliant, Code.org, Scratch, Chess.com, Lichess |
| Tabletop Online | Board Game Arena, Tabletop Simulator (Steam), Vassal, Roll20, PlayingCards.io |
Reply with your preferences — I'll give targeted recommendations.