Modern rigging is the new way to quickly setup a rig using Asset Warp tool, rotate the bones or warp the joints to create poses and apply a classic tween to automatically create the in-betweens to form a smooth animation. 

Following are some of the capabilities enabled in the Modern Rigging workflow:

• Ability to create Hard & soft bones using Asset warp tool
• Ability to change bone type from hard to soft & vice-versa
• Ability to change the mesh density to balance between the warp quality and performance
• Ability to Add/remove the pin without breaking the tween
• Ability to freeze joint
• Ability to rotate the bone or specify the desired angle for the selected bone in Properties panel
• Dedicated Tool tab in Properties panel for Asset warp tool
• Option to enable/disable pin propagation across keyframes and more
  

For more details, see Modern Rigging

Propagate the scale, skew, flip transformations now in addition to translation and rotation in parenting.

For more details, see Scale, Skew and Flip in Parenting