  We search the archival Zwicky Transient Facility public survey for rapidly
evolving transient (RET) candidates based on well-defined criteria between 2018
May and 2021 December. The search yielded 19 bona-fide RET candidates,
corresponding to a discovery rate of $\sim 5.2$ events per year. Even with a
Galactic latitude cut of $20^\circ$, 8 of the 19 events ($\sim 42$%) are
Galactic, including one with a light-curve shape closely resembling that of the
GW170817 kilonova (KN). An additional event is a nova in M31. Four out of the
19 events ($\sim 21$%) are confirmed extragalactic RETs (one confirmed here for
the first time) and the origin of 6 additional events cannot be determined. We
did not find any extragalactic events resembling the GW170817 KN, from which we
obtain an upper limit on the volumetric rate of GW170817-like KNe of $R \le$
2400 Gpc$^{-3}$ yr$^{-1}$ (95% confidence). These results can be used for
quantifying contaminants to RET searches in transient alert streams,
specifically when searching for kilonovae independently of gravitational-wave
and gamma-ray-burst triggers.
