Useful Add-Ons. #

Blender ships with a lot of features that it keeps hidden, that can easily be activated by going into to File>Preferences>Add-Ons menu. Third party developers can create their own add-ons, and there is a marketplace of individuals writing such software.

In no particular order

Blender Add-Ons #

Extra Objects in the add menu.
A.N.T. Landscape can generate terrains.
LoopTools contains many useful features, like circular-izing a selection of vertices.
Node Wrangler everyone who uses nodes uses node wrangler.

Node Wrangler Addon

Third-Party Free Add-Ons #

Noodler for managing nodes.
Camera Shakify for adding realistic camera shake.
Edge Flow for working with multiple edge loops.
BlenderGIS for working with real world satellite/terrain data.
Cut Corner cuts corners.
Animation Nodes An entire system for animating with nodes.