A continuously in-development engine I am creating for a current game project of mine, which I am making in GameMaker: Studio. This engine might change drastically through time, or it may not change at all - it depends on what I need in my game personally.
The engine is containing the physics part of my game, and currently has these features:
Entity physics - Simple AI - Static and dynamic blocks - Moving platforms - Bouncing blocks - Pushable blocks - Ghost blocks (including ghost moving platforms) - Ice
Basically the engine is based around two main kinds of objects; entities (par_entity) and solids (par_solid_static) + a cross-breed between them, the dynamic solid (par_solid_dynamic). Everything else is pretty much just sub-types of these. Entities utilizes some nice physics codes, which allows them to interact easily with each other, and makes the system easy to build upon.