  We discuss some recent developments in the theory of free boundary problems,
as obtained in a series of papers in collaboration with L. Caffarelli, A.
Karakhanyan and O. Savin.
  The main feature of these new free boundary problems is that they deeply take
into account nonlinear energy superpositions and possibly nonlocal functionals.
  The nonlocal parameter interpolates between volume and perimeter functionals,
and so it can be seen as a fractional counterpart of classical free boundary
problems, in which the bulk energy presents nonlocal aspects.
  The nonlinear term in the energy superposition takes into account the
possibility of modeling different regimes in terms of different energy levels
and provides a lack of scale invariance, which in turn may cause a structural
instability of minimizers that may vary from one scale to another.
