Ultra luminous X-ray (ULX) sources are off-nuclear extra-galactic X-ray binary systems with an apparent isotropic luminosity that exceeds the Eddington limit for an accretion powered, stellar mass black hole. Given their high luminosity ULXs were always thought to be ideal systems to search for the elusive intermediate-mass black holes. Remarkably, within the last years there has been undisputed evidence that at least a few of these systems are powered by accreting highly magnetized neutron stars (NS), these are known as ULX pulsars or ULXPs. Still, many major open questions about ULXPs remain: are the observed luminosities probes of high accretion rates, or are they a result of a highly anisotropic (beamed) emission? Are strong magnetic fields necessary to power the engines of ULXPs? For a handful of individual sources (i.e. the closest and brightest) it demonstrated that super-Eddington accretion is possible, barring implications for the X-ray binary population and their impact on their environment. In this talk I will focus on ULXPs as laboratories to study super-Eddington accretion by presenting observational properties that could provide answers to the aforementioned open questions. On one hand spectral studies demonstrate similarities between non-pulsating ULXs and typical X-ray pulsars, thus demonstrating that the majority of ULXs could host magnetized NSs as their engines. On the other hand, temporal studies of ULXPs provide some of the most accurate constraints on the NSs magnetic fields and help us study outflows from these extreme accretors. All the above have demonstrated that strong beaming is not required and that the mass accretion rates are indeed super-Eddington.
