  NGC 300 ULX1 is the fourth to be discovered in the class of the
ultra-luminous X-ray pulsars. Pulsations from NGC 300 ULX1 were discovered
during simultaneous XMM-Newton / NuSTAR observations in Dec. 2016. The period
decreased from 31.71 s to 31.54 s within a few days, with a spin-up rate of
-5.56 x 10^{-7} s s^{-1}, likely one of the largest ever observed from an
accreting neutron star. Archival Swift and NICER observations revealed that the
period decreased exponentially from ~45 s to ~17.5 s over 2.3 years. The pulses
are highly modulated with a pulsed fraction strongly increasing with energy and
reaching nearly 80% at energies above 10keV. The X-ray spectrum is described by
a power-law and a disk black-body model, leading to a 0.3-30 keV unabsorbed
luminosity of 4.7 x 10^{39} erg s^{-1}. The spectrum from an archival
XMM-Newton observation of 2010 can be explained by the same model, however,
with much higher absorption. This suggests, that the intrinsic luminosity did
not change much since that epoch. NGC 300 ULX1 shares many properties with
supergiant high mass X-ray binaries, however, at an extreme accretion rate.
