In short, it is a 2D game engine written in Nim. Hangover started as a full rewrite of a game engine called gin, which was inspired by Monogame. At the point of writing this, Hangover has been inspired by Unity, GodotNim and more.
There are little to no reasons to use hangover as it was just made as a side project, but these are the reasons I use it.
Hangover supports a ec system based off unitys. Allowing an "easier" transition from unity to Hangover.
Hangover uses nims macros to define systems, allowing for cleaner code.