Rockman Copy System is a video game engine that aims to replicate the physics of the Rockman (Mega Man in the West) games as accurately as possible. So far, Rockman, Rockman 2 and Rockman 3's physics have been implemented.
It's written in C++ using SDL 1.2 and SDL 2.0 and is available for Windows (95 and up) and the PlayStation Portable. It's open source and subject to the terms of the Mozilla Public License, v. 2.0.
Note: while the DLL file for SDL 1.2 is included in the archive for Windows, the DLL file for SDL 2.0 has to be downloaded separately.