  Hubble Space Telescope's (HST) Space Telescope Imaging Spectrograph (STIS)
targeted 556 stars in a long-running program called Next Generation Spectral
Library (NGSL) via proposals GO9088, GO9786, GO10222, and GO13776. Exposures
through three low resolution gratings provide wavelength coverage from 0.2 $<
\lambda <$ 1 $\mu$m at $\lambda/\Delta\lambda\sim$ 1000, providing unique
coverage in the ultraviolet (UV). The UV grating (G230LB) scatters red light
and this results in unwanted flux that becomes especially troubling for cool
stars. We applied scattered light corrections based on
\cite{2022stis.rept....5W} and flux corrections arising from pointing errors
relative to the center of the 0\farcs2 slit. We present 514 fully reduced
spectra, fluxed, dereddened, and cross-correlated to zero velocity. Because of
the broad spectral range, we can simultaneously study H$\alpha$ and Mg II
$\lambda$2800, indicators of chromospheric activity. Their behaviours are
decoupled. Besides three cool dwarfs and one giant with mild flares in
H$\alpha$, only Be stars show strong H$\alpha$ emission. Mg2800 emission,
however, strongly anti-correlates with temperature such that warm stars show
absorption and stars cooler than $5000 \: \! \rm{K}$ universally show
chromospheric emission regardless of dwarf/giant status or metallicity.
Transformed to Mg2800 flux emerging from the stellar surface, we find a
correlation with temperature with approximately symmetric astrophysical
scatter, in contrast to other workers who find a basal level with asymmetric
scatter to strong values. Unsurprisingly, we confirm that Mg2800 activity is
variable.
