Neutron stars are nature's
ultimate extreme machines. They provide
a glimpse at physical conditions that exist nowhere else in the
universe
and provide a way to "crash test" our current understanding of physics.
Recent X-ray observations from space, many made with NASA observatories,
have given us a new window onto these objects. I will provide a fast
paced
tour of some of these recent findings, emphasizing observations done
with
the Rossi X-ray Timing Explorer, and discuss what they are telling us
about neutron stars and fundamental physics.