All of my work is built on top of a slew of other open/open-source/free tools and resources … like:
Defold — an open-source game engine that lets you write games in the Lua programming language
Kenney — an amazing set of art (& audio) resources that are open/free for everyone to use
Pexels — a great resource for photos and images- Special thanks to Jolo Diaz for the blue turtle hatchling photo on the cover
Open Game Art — another great resource for open/free art- flaticons.net — another great source of icon (b/w) images for a variety of objects/ui-actions/etc.
We Love Indies / Dynamedion — great sounds and music at reasonable prices (free for prototyping new apps)
Zapsplat — great sounds, many for free
Krita — free/open-source drawing/image manipulation program
GNU Image Manipulation Program — free/open-source image creation and manipulation tool