Grasscutter
A server software reimplementation for a certain anime game
...The project allows users to run a compatible server environment for specific supported game client versions, but it is not actively maintained in the same way it once was. Current documentation warns that version matching matters and that support is limited, especially beyond the older supported release range. Grasscutter is most relevant to developers interested in reverse engineering, server emulation, game protocol research, and modding communities. Because it interacts with proprietary game clients and services, it should be used only in lawful, authorized, and non-commercial contexts.