In this talk I discuss certain string flux backgrounds that lead to non-commuting closed string coordinates. The role of T-duality and non-geometric spaces (T-folds) play an important role in this discussion. Finally we also mention the underlying and possibly non-associative algebraic structure as well as new Heisenberg uncertainty relations, which arise in this context.

Maximal and non-maximal supergravities in three spacetime dimensions allow for a much richer variety of semisimple, non-semisimple and even complex gaugings than supergravities in four and more spacetime dimensions. In particular, most of these models do not appear to possess a geometrical origin from higher dimensions. In this talk I will review the construction of these theories, concentrating on the most interesting case of maximal (N=16) supergravity, and emphasizing the key role of the so-called embedding tensor in the construction. I will then discuss some of their properties, including the equivalence of Yang-Mills gaugings with certain Chern-Simons gaugings. Finally, as one special application, I will briefly explain how to derive the currently popular rigidly superconformal D=3 models (with N\leq 8) as flat space limits of certain gauged supergravities

I will discuss ways of obtaining mass hierarchies in string theory, realizing the main phenomenological scenaria that have been proposed in recent years, such as large extra dimensions, large warping factors and large number of particle species. Holography can be used to study non trivial realizations, extracting the main signatures that can be tested in particle colliders.