If you're looking for an open-source way to rapidly and easily create pixel art images for your game, Pixelfy is a great option. This AI-powered tool offers a range of styles for backgrounds and character art, along with features like prompt builders, grid size control and color palette management. Its open-source nature and GitHub hosting means it's available for creative pros who want to modify it to suit their needs.
Another alternative is Snowpixel, a generative media toolkit that can also be used to create pixel art from text prompts. While it's designed to handle a wider range of media generation, including video and music, its pixel art abilities can be useful for game developers who need art that's flexible and fast to create.
If you're specifically interested in game assets, the AI Game Assets Generator is a powerful tool that uses AI to generate characters, props and backgrounds. You can describe the assets you want and the tool will generate them on the fly, making it a good choice for anyone looking to speed up their asset creation.