Free Blender Plug-ins

Edge Flow:

This plug-in finds the best curvature position between two edge loops and set's the selected edge loop's position according to the other loops around it. So it kind of works like Looptools relax function, but some find this better.

Click on the following link, to learn more about how to use the Set Flow plug-in: Edge Flow

Download link to Edge Flow plug-in

Looptools:

This is an other interesting plug-in which comes free Blender. Use it especially to make:

• circle from your selected vertices.
• relax the tension between the vertices.
• space the vertices evenly.
  No need for a link for the plug-in as it comes bundled with Blender. You just need to enable the add-on in preferences.

Click on the following link, to learn more about how to use the Looptools plug-in: Looptools

Easy HDRI:

This is a very nice plug-in that helps you to switch between HDRI environments quickly inside your project to see and find the best one for your needs. Definitely suggest using it.

Click on the following link, to learn more about how to use the Easy HDRI plugin: Easy HDRI