  Non-geometric frames in string theory are related to the geometric ones by
certain local O(D,D) transformations, the so-called $\beta$-transforms. For
each such transformation, we show that there exists both a natural field
redefinition of the metric and the Kalb-Ramond two-form as well as an
associated Lie algebroid. We furthermore prove that the all-order low-energy
effective action of the superstring, written in terms of the redefined fields,
can be expressed through differential-geometric objects of the corresponding
Lie algebroid. Thus, the latter provides a natural framework for effective
superstring actions in non-geometric frames. Relations of this new formalism to
double field theory and to the description of non-geometric backgrounds such as
T-folds are discussed as well.
