Stickman Animation Software - Download
This is the software algorithm that was the beginning of Stickman, now 7 years ago.
Bone simulation keeps two control points in constant distance.
Given two points, p1, p2 and constant distance n (scalar).
diff = p1 - p2
delta = n - |diff| (|diff| is the absolute value of diff, length of vector)
diff *= delta / |diff|
p1 += diff * delta * 0.5
p2 -= diff * delta * 0.5
You can replace 0.5 with 0.4 to have less stiffer simulation.
Iterate for each bone many times (10+)
Simulation with rigids, feedback and rope are company secrets, so I can't tell you.