  We investigate the nature of CXOU J005440.5-374320 (J0054), a peculiar bright
($\sim$$4\times10^{39}$ erg/s) and soft X-ray transient in the spiral galaxy
NGC 300 with a 6-hour periodic flux modulation that was detected in a 2014
Chandra observation. Subsequent observations with Chandra and XMM-Newton, as
well as a large observational campaign of NGC 300 and its sources performed
with the Swift Neil Gehrels Observatory, showed that this source exhibits
recurrent flaring activity: four other outbursts were detected across $\sim$8
years of monitoring. Using data from the Swift/UVOT archive and from the
XMM-Newton/OM and Gaia catalogues, we noted the source is likely associated
with a bright blue optical/ultraviolet counterpart. This prompted us to perform
follow-up observations with the Southern African Large Telescope in December
2019. With the multi-wavelength information at hand, we discuss several
possibilities for the nature of J0054. Although none is able to account for the
full range of the observed peculiar features, we found that the two most
promising scenarios are a stellar-mass compact object in a binary system with a
Wolf$-$Rayet star companion, or the recurrent tidal stripping of a stellar
object trapped in a system with an intermediate-mass ($\sim1000$ $M_\odot$)
black hole.
