  We present ground-based and \textit{Swift} observations of iPTF16fnl, a
likely tidal disruption event (TDE) discovered by the intermediate Palomar
Transient Factory (iPTF) survey at 66.6 Mpc. The lightcurve of the object
peaked at absolute $M_g=-17.2$ mag. The maximum bolometric luminosity (from
optical and UV) was $L_p~\simeq~(1.0\,\pm\,0.15) \times 10^{43}$ erg/s, an
order of magnitude fainter than any other optical TDE discovered so far. The
luminosity in the first 60 days is consistent with an exponential decay, with
$L \propto e^{-(t-t_0)/\tau}$, where $t_0$=~57631.0 (MJD) and $\tau\simeq 15$
days. The X-ray shows a marginal detection at $L_X=2.4^{1.9}_{-1.1}\times
10^{39}$ erg/s (\textit{Swift} X-ray Telescope). No radio counterpart was
detected down to 3$\sigma$, providing upper limits for monochromatic radio
luminosity of $\nu L_{\nu} < 2.3\times10^{36}$ erg/s and $\nu L_{\nu}<1.7\times
10^{37}$ erg/s (VLA, 6.1 and 22 GHz). The blackbody temperature, obtained from
combined \textit{Swift} UV and optical photometry, shows a constant value of
19,000 K. The transient spectrum at peak is characterized by broad He II and
H$\alpha$ emission lines, with an FWHM of about 14,000 km/s and 10,000 km/s
respectively. He I lines are also detected at $\lambda\lambda$ 5875 and 6678.
The spectrum of the host is dominated by strong Balmer absorption lines, which
are consistent with a post-starburst (E+A) galaxy with an age of $\sim$650 Myr
and solar metallicity. The characteristics of iPTF16fnl make it an outlier on
both luminosity and decay timescales, as compared to other optically selected
TDEs. The discovery of such a faint optical event suggests a higher rate of
tidal disruptions, as low luminosity events may have gone unnoticed in previous
searches.
