  With a column density log N(OVI) = 14.95+/-0.05, the OVI absorber at
z_abs~0.2028 observed toward the QSO PKS0312-77 (z_em=0.223) is the strongest
yet detected at z<0.5. At nearly identical redshift (z_abs=0.2026), we also
identify a Lyman limit system (LLS, log N(HI)=18.22). Combining FUV and NUV
spectra of PKS0312-77 with optical observations of galaxies in the surrounding
field (15'x32'), we present an analysis of these absorbers and their connection
to galaxies. The observed OI/HI ratio and photoionization modelling of other
low ions indicate the metallicity of the LLS is [Z/H]_LLS=-0.6 and that the LLS
is nearly 100% photoionized. In contrast, the OVI-bearing gas is collisionally
ionized at T~(3-10)x10^5 K as derived from the high-ion ratios and profile
broadenings. Our galaxy survey reveals 13 (0.3<L/L*<1.6) galaxies at \rho<2
h^{-1}_{70} Mpc and |\delta v|<1100 km/s from the LLS. A probable origin for
the LLS is debris from a galaxy merger, which led to a 0.7L* galaxy
([Z/H]_gal=+0.15) at\rho~38 h^{-1}_{70} kpc. Outflow from this galaxy may also
be responsible for the supersolar ([Z/H]_abs=+0.15), fully ionized absorber at
z_abs=0.2018 (-190 km/s from the LLS). The hot OVI absorber likely probes
coronal gas about the 0.7 L* galaxy and/or (~0.1 keV) intragroup gas of a
spiral-rich system. The association of other strong OVI absorbers with LLS
suggests they trace galactic and not intergalactic structures.
