Unity - The multiplatform game creation tools for everyone.
iOSStash - A huge collection of app-related tools
Godot Engine - Feature-packed 2D and 3D open source game engine.
iOS Cookies - A hand curated collection of iOS libraries written in Swift
Blender - Blender is the open source, cross platform suite of tools for 3D creation.
AppToolkit - AppToolkit provides tools to build iOS screenshots, app landing pages, and to monitor app reviews