This is a quick demo of the 2D game engine I'm making in Common Lisp called Ghostie (github.com/orthecreedence/ghostie). This is a simple forest level, with a platform that moves when the player steps on it, and the ability to add boxes to the level.
Ghostie makes it easy to design levels and objects both visually and physically. It uses the excellent Chipmunk physics engine (chipmunk-physics.net/) for physics simulation, and uses SVG files to describe the appearance of levels and objects. Using SVG means that armed with a good editor (Illustrator, Inkscape, etc) and a bit of knowledge on how levels are set up in the engine, you can create beautiful levels and characters fairly simply.
Please note that this engine is currently in alpha. I'm constantly changing/adding to it. I'm releasing the video as a preview of what's to come.