Plugins
Flip Fluids
The FLIP Fluids addon is a tool that helps you set up, run, and render liquid simulation effects
Paid76$
Gaffer
A light-manager add-on for Blender with all the HDR's from HDRIHaven
Free
Hard Ops and Boxcutter
The best tool for helping you with hard surface modeling.
Paid38$
Lily Surface Scraper
Import shaders end environments in Blender from a single URL