  Two recent observations of the nearby galaxy NGC 6946 with NuSTAR, one
simultaneous with an XMM-Newton observation, provide an opportunity to examine
its population of bright accreting sources from a broadband perspective. We
study the three known ultraluminous X-ray sources (ULXs) in the galaxy, and
find that ULX-1 and ULX-2 have very steep power-law spectra with
$\Gamma=3.6^{+0.4}_{-0.3}$ in both cases. Their properties are consistent with
being super-Eddington accreting sources with the majority of their hard
emission obscured and down-scattered. ULX-3 (NGC 6946 X-1) is significantly
detected by both XMM-Newton and NuSTAR at $L_{\rm X}=(6.5\pm0.1)\times10^{39}$
erg s$^{-1}$, and has a power-law spectrum with $\Gamma=2.51\pm0.05$. We are
unable to identify a high-energy break in its spectrum like that found in other
ULXs, but the soft spectrum likely hinders our ability to detect one. We also
characterise the new source, ULX-4, which is only detected in the joint
XMM-Newton and NuSTAR observation, at $L_{\rm X}=(2.27\pm0.07)\times10^{39}$
erg s$^{-1}$, and is absent in a Chandra observation ten days later. It has a
very hard cut-off power-law spectrum with $\Gamma=0.7\pm0.1$ and $E_{\rm
cut}=11^{+9}_{-4}$ keV. We do not detect pulsations from ULX-4, but its
transient nature can be explained either as a neutron star ULX briefly leaving
the propeller regime or as a micro-tidal disruption event induced by a
stellar-mass compact object.
