The best alternatives to Game Builder are Buildbox, Minecraft, and Minecraft: Pocket Edition. If these 3 options don't work for you, we've listed a few more alternatives below.
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Buildbox is a new video game maker that is extremely easy to use. Using this video game software, anyone to design amazing games for mobile, console and PC.
Bitmelo is a game editor and engine for making small pixel art games. You can code, draw tiles and tilemaps, design sound effects, view the documentation, and playtest your game, all without having to break focus by switching applications.