The latest and greatest in performance, sorry I mean antiperformance mods!
Using the unholy merged power of mixins and events Darmstadtium manages to at least halve your FPS by ensuring that more chunks that really shouldn't be rendered, are rendered! Depending on the config options (configurable at config/darmstadtium-client.toml) Darmstadtium will show chunks that Minecraft thinks are hidden by other chunks, and chunks that are not in your field of view!
But why you ask?! The primary purpose is to allow for use of abnormal resource packs that warp your world into strange, never seen before shapes such as a... sphere! If you wish to try some of these for yourself find a selection of them here: https://gist.github.com/williambl/4a4d74d1b72da350d96d7859b6b70e57