  We present some recent measurements performed using 514 fb-1 of $e^+e^-$
collisions collected with the BaBar detector at the PEP-II asymmetric collider
at SLAC. First we present a study of the decay tau -> K K_S nu, we measure the
branching fraction B(tau -> K K_S nu), the mass spectrum of the K K_S system
and obtain the spectral function. Our results are in agreement with and improve
previous measurements. We then report a search for a dark boson A' produced in
the reaction e+e- -> gamma A' in invisible final states A' -> chi anti-chi . We
find no evidence for such processes and set 90% confidence level upper limits
on the coupling strength of A' as a function of the A' mass m'. In particular,
our limits exclude the values of the A' coupling suggested by the dark-photon
interpretation of the muon (g-2) anomaly. Finally we report the search for a
light non-Standard Model gauge boson A' coupling only to the second and third
lepton families. Our results significantly improve current limits and further
constrain the remaining region of the allowed parameter space.
