BoneDynamics  is a  blender addon that allows you to add physics to bones.

Check my youtube page for instructions on how to use this properly :

https://www.youtube.com/watch?v=b4qt2jOmu9Q&list=PLRUmha6ifE53xz6pL4gTV4Pyih7BhCSvM

https://youtu.be/b_K1S_BsjX8

There's also an official discord server where you can get tips and some help :

https://discord.gg/JaeVteJFZT

The free version is fully functional, but lacks features that improves the workflow 

Features:

• Tweak  one or multiple bones physics parameters on the fly (Pro)
• collision on the entire bone
• Bones react to movement and collision.
• Super easy to setup.
• Ability to stretch bones.
• Ability to make a bone chain. (Pro)
• Easy to tweak (it uses soft body under the hood).
• Upcoming updates for free.
• Enhanced baking system (Pro)
• Dynamic Parenting (Pro)
• Displacement (Pro)

There is a free version if you want to try it before you buy it, the free version has limited features, but it is completely usable and free

CHANGELOG:

• 0.1.0:

-Initial release.

• 0.1.1:

-Added the ability to pick the size of the object controlling the bone.

• 0.1.5:

- Better errors handling.

- Naming collision bug fixed.

- Reactive UI values based on selection.

- Playback performance improvements.

• 0.1.6:

- Fix bad spawn position

• 0.1.7:

- Fixed Foreign language Error.

- Instant updates when you tweak parameters.

- New Presets manager feature.

- Performance improvements.

- Better UI

• 1.0.4:  

- Fixed Foreign language Error.

- New chain mode and cloth Mode (tutorial soon)

• 1.0.6:  

- Fixed bone layers consistency bug.

- No need to select the active bone anymore

• 1.0.8:  

- Minor bug fixes.

- Chain mode tweak

• 1.2.1:  

- Major bug fixes.

- Ability to use it with linked armatures (library overrides).

• 1.2.5:  

- Dynamic Bone list with shortcuts, ON / OFF , selection.

- Tweakable frame step when you bake the animation.

• 1.3.5:  

- FIxed the crash when you undo

- New displacement mode

• 1.4.0:  

- FIxed baking resolution not working

- New dynamic parent mode

- Ability to keyframe dynamic bones

• 1.4.5:  

- Multiple Bug fixes 

- New Transfer animation feature

- Ability to keyframe dynamic bones