Skyrim Script Extender (SKSE)
This is not a mod but a plugin that some mods are dependent on. It is very important to read the mod requirements before installing and confirm if SKSE is required or not.
It’s a love/hate relationship with this plugin for many so it’s an individual choice and installation is easy. When you run LOOT for a new game, you will be told if there is a new version out. How can we argue with that?
SKSE is basically one of the mod builder’s tools and adds new script functions to the Papyrus language Skyrim uses and this allows modders to create mods that would be otherwise impossible to do.