FREEIK

Features:

• Turn basic armature into the animation ready rig in a couple of clicks
• A more intuitive way to pose and animate a model
• Different posing modes
• Bones can be pinned
• You can change bones hierarchy on the fly
• Character skeleton may have loops
• The rig can be split into parts during the animation
• You can animate objects in the same way as bones
• Most of the features can be accessed from the pie menu

Development plan:

• Rewrite solver in C.

• Improve performance ( it's quite low now, see Optimization section of manual)
• Implement constraint limits
• Tools for face rigging
• Make solver take into account Blender constraints
• Retargeting tools
• Bunch of features for posing and animation that are hard to describe using words

If you have any ideas, questions or anything else to say, you can use this thread

Also, check out my GitHub and Artstation