NXEngine has been ported to Nintendo Switch by carstene1ns and is a reimplementation of the original Cave Story / Doukutsu Monogatari game engine, using its data files. The game itself is a pretty famous side-scrolling platformer from 2004. This release has nothing to do with Cave Story+ (published by Nicalis and being an actual, official Switch game).

Thanks to Nintendomax for the news!