They are all supersymmetric. Their worldvolume dynamics is described by non-gravitational theories, usually gauge theories. Some simple explanations and related links can be found at this address . They are the only kind of non-perturbative structure that may exist at the electroweak scale and has a chance to be observed in future high energy physics experiments. There is activity in the study of various MSSM processes at LEP and NLC energies, probing the Higgs and SuSy sectors.
Most recent work is on four-fermion production at colliders.
Monte Carlo generators are also developed.