  We report a new Fast Radio Burst (FRB) discovered in real-time as part of the
UTMOST project at the Molonglo Observatory Synthesis Radio Telescope (MOST).
FRB170827 is the first detected with our low-latency ($< 24$ s),
machine-learning-based FRB detection system. The FRB discovery was accompanied
by the capture of voltage data at the native time and frequency resolution of
the observing system, enabling coherent dedispersion and detailed off-line
analysis, which have unveiled fine temporal and frequency structure. The
dispersion measure (DM) of 176.80 $\pm$ 0.04 pc cm$^{-3}$, is the lowest of the
FRB population. The Milky Way contribution along the line of sight is $\sim$ 40
pc cm$^{-3}$, leaving an excess DM of $\sim$ 145 pc cm$^{-3}$. The FRB has a
fluence $>$ 20 $\pm$ 7 Jy ms, and is narrow, with a width of $\sim$ 400 $\mu$s
at 10$\%$ of its maximum amplitude. However, the burst shows three temporal
components, the narrowest of which is $\sim$ 30 $\mu$s, and a scattering
timescale of $4.1 \pm 2.7$ $\mu$s. The FRB shows spectral modulations on
frequency scales of 1.5 MHz and 0.1 MHz. Both are prominent in the dynamic
spectrum, which shows a very bright region of emission between 841 and 843 MHz,
and weaker, patchy emission across the entire band. We show the fine spectral
structure could arise in the FRB host galaxy, or its immediate vicinity.
