The primary parts of the development stack include:
Haxe is a cross platform open source programming language with a high-level strictly typed language capable of being compatible to multiple languages or runtimes.
A high performance open source game focused virtual machine for Haxe.
The confusingly named Haxe IDE is essentially a full blown level editor capable of creating 2D and 3D games.
A game focused database engine with a built in tilemap editor. You can learn more about the CastleDB here.
Combined together you get a complete, battletested and production ready game engine with several high quality shipped titles under its belt. You can learn more about the entire technology stack in the video below.