MARSLite was supposed to be a 2D only version of MARS that used the same engine design philosophy that MARS uses. However, now that MARS is going to support 2D natively, I don't know if this project will continue.
Currently it supports input binding, and has a very basic rendering wrapper for SFML. It also includes a resource manager/loader. So it could be used as a starting point of a 2D game engine.