See: Description
Class  Description 

ConeJoint 
From bullet manual:
To create ragdolls, the cone twist constraint is very useful for limbs like the upper arm. 
HingeJoint 
From bullet manual:
Hinge constraint, or revolute joint restricts two additional angular degrees of freedom, so the body can only rotate around one axis, the hinge axis. 
PhysicsJoint 
PhysicsJoint  Basic Phyiscs Joint

Point2PointJoint 
From bullet manual:
Point to point constraint, also known as ball socket joint limits the translation so that the local pivot points of 2 rigidbodies match in worldspace. 
SixDofJoint 
From bullet manual:
This generic constraint can emulate a variety of standard constraints, by configuring each of the 6 degrees of freedom (dof). 
SliderJoint 
From bullet manual:
The slider constraint allows the body to rotate around one axis and translate along this axis. 