Useful Add-Ons.

Blender ships with a lot of features that it keeps hidden, which 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.

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.