W Algebras, W Gravities and their Moduli Spaces
  By generalizing the Drinfel'd--Sokolov reduction we construct a large class of W algebras as reductions of Kac--Moody algebras. Furthermore we construct actions, invariant under local left and right W transformations, which are the classical covariant induced actions for W gravity. Talk presented by T. Tjin at the Trieste Summerschool on strings and related topics. 
F. A. Bais, T. Tjin, P. van Driel, J. de Boer and J. Goeree