  We report on FORS2 spectroscopy aiming at the identification of four Galactic
Plane sources discovered by $INTEGRAL$, IGR J18088-2741, IGR J18381-0924, IGR
J17164-3803, and IGR J19173+0747, complemented by $XMM$-$Newton$ spectroscopy
for IGR J18381-0924. The presence of broad emission lines of neutral H and He
and a flat Balmer decrement H{\alpha}/H{\beta} show that IGR J18088-2741 is a
cataclysmic variable located beyond 8 kpc. For IGR J18381-0924, the detection
of red-shifted H{\alpha} and neutral O emission signatures and the absence of
narrow forbidden emission lines point towards a low-luminosity Seyfert 1.9
nature at $z=0.031\pm0.002$. Its $XMM$-$Newton$ spectrum, best-fit by an
absorbed ${\Gamma}=1.19\pm0.07$ power law combined with a
$z=0.026_{-0.016}^{+0.008}$ red-shifted iron emission feature, is in agreement
with this classification. The likely IGR J17164-3803 optical counterpart is an
M2 III star at 3 to 4 kpc which, based on the X-ray spectrum of the source, is
the companion of a white dwarf in an X-ray faint symbiotic system. Finally, we
challenge the accepted identification of IGR J19173+0747 as an high mass X-ray
binary. Indeed, the USNO optical counterpart is actually a blend of two objects
located at the most likely 3 kpc distance, both lying within the error circle
of the Swift position. The first is a cataclysmic variable, which we argue is
the real nature of IGR J19173+0747. However, we cannot rule out the second one
that we identify as an F3 V star that, if associated to IGR J19173+0747, likely
belongs to a quiescent X-ray binary.
