I have a spent a lot of time in finding perfect references for human figures. We generally use mannequins for that purpose but I thought a web version will be more accessible as you can download the reference pose as an image and use that too.
I used three.js to build https://getreference.vercel.app/ for that purpose. There are lot of ideas like inverse kinematics in the plan.
The source code is available on GitHub and can be found here: https://github.com/ritz078/reference