Skyrim Reloaded mainly modifies the rendering pipeline, adding new features and providing screen effects not supported in vanilla Skyrim.
This project raises from Oblivion Reloaded, implementing in Skyrim a lot of new features.
Skyrim Reloaded gives the possibility to replace the vanilla shaders and supports several built-in effects, but it has also a custom engine to support any new own effect. Skyrim Reloaded can be called a mod, but it is not a "normal" mod but a real "code patch". It basically upgrades Skyrim to a new version. It works/modifies directly on the Creation Engine, so it is fast, stable and with a very low performance impact (basically nothing).
I understand that a lot of people have been waiting a long time for this.
It appears to be doing the magic through an SKSE dll and a number of shaders. Configurable via ini. ESP and scripts enable a hotkey for screenshots that automatically don't contain the UI. Possibly something else. Full manual is in the download which I haven't read yet :)