I noticed an omission on this list was Minecraft. Today, the game of course has thousands of engineers working on the various versions of the game due to its success. But in the beginning (and throughout Alpha/Beta and during the beginning years of its 1.0 development) it was built on a hacked-together Java LIBJDX 2.0-based engine.
Here's the first video uploaded by Notch when he first embarked on a new "Cave game": https://www.youtube.com/watch?v=UMpv5kZ9-rE (the original video is blocked in the US for some reason)
An interesting side-effect of this technical decision was that the game was heavily moddable. Java byte code is relatively easy to decompile, and class files easily modularize the various components of the game. So installing a mod amounted to un-zipping the minecraft.jar file and replacing .class files with modded ones. In fact, this is still how modding works in the Java version of the game.
Here's the first video uploaded by Notch when he first embarked on a new "Cave game": https://www.youtube.com/watch?v=UMpv5kZ9-rE (the original video is blocked in the US for some reason)
An interesting side-effect of this technical decision was that the game was heavily moddable. Java byte code is relatively easy to decompile, and class files easily modularize the various components of the game. So installing a mod amounted to un-zipping the minecraft.jar file and replacing .class files with modded ones. In fact, this is still how modding works in the Java version of the game.