RetroArch - RetroArch is a frontend for emulators, game engines and media players.
Figma - Team-based interface design, Figma lets you collaborate on designs in real time.
mGBA - mGBA is an open source emulator of the Game Boy Advance. The goals are speed and accuracy.
Visage - Visage is a new platform that enables non-designers to easily create beautiful, on-brand visual content such as data visualization, reports & much more
DeSmuME - DeSmuME is a freeware emulator for the NDS roms & Nintendo DS Lite games created by YopYop156.
Start on Android by Google - Developer program to optimize your app before you launch