HaxeFlixel
Free, cross-platform 2D game engine powered by Haxe and OpenFL
...HaxeFlixel emphasizes ease of use and rapid development for 2D games — ideal for pixel-art platformers, card games, puzzles, or 2D action games. It includes common utilities and abstractions for sprites, animations, input handling, game loops, asset management, and state transitions, making it easier to build a complete game without reinventing core infrastructure. Because of this, it has been used for successful indie games and prototypes alike, and remains a popular choice among developers.