RGBDS is the community's preferred Game Boy and Game Boy Color assembler package, free and open-source. Find here documentation and install instructions.

Flexible level editor

A free and open-source 2D game engine.

Pulp is a click-and-place, fun, quirky game studio for Playdate. Make a game with no code, or maybe a little code.

A free, open source, project oriented level editor made for indie game developers by indie game developers.

a tool for drawing and assembling graphical hypertext games

GB BASIC is a retro Fantasy Console that generates ROMs compatible with the popular handheld game console.

A quick and easy to use drag and drop retro game creator for your favourite handheld video game system.

Downpour is the best app for making games on your phone. Collage together photos, drawings and text, and then connect them into an interactive story. It's genuinely quick and easy to use — you can make a game before your tea has gone cold. Once you've made a game with Downpour, what then? You can share it with your friends inside the app, or post the link for anyone to play.

bipsi is a tool for making small games where a character explores a world and interacts with its inhabitants.