  In this paper, we describe the "Medium Bands, Mega Science" JWST Cycle 2
survey (JWST-GO-4111) and demonstrate the power of these data to reveal both
the spatially-integrated and spatially-resolved properties of galaxies from the
local universe to the era of cosmic dawn. Executed in November 2023,
MegaScience obtained ~30 arcmin^2 of deep multiband NIRCam imaging centered on
the z~0.3 Abell 2744 cluster, including eleven medium-band filters and the two
shortest-wavelength broad-band filters, F070W and F090W. Together, MegaScience
and the UNCOVER Cycle 1 treasury program provide a complete set of deep (~28-30
mag) images in all NIRCam medium- and broad-band filters. This unique dataset
allows us to precisely constrain photometric redshifts, map stellar populations
and dust attenuation for large samples of distant galaxies, and examine the
connection between galaxy structures and formation histories. MegaScience also
includes ~17 arcmin^2 of NIRISS parallel imaging in two broad-band and four
medium-band filters from 0.9-4.8um, expanding the footprint where robust
spectral energy distribution (SED) fitting is possible. We provide example SEDs
and multi-band cutouts at a variety of redshifts, and use a catalog of JWST
spectroscopic redshifts to show that MegaScience improves both the scatter and
catastrophic outlier rate of photometric redshifts by factors of 2-3.
Additionally, we demonstrate the spatially-resolved science enabled by
MegaScience by presenting maps of the [OIII] line emission and continuum
emission in three spectroscopically-confirmed z>6 galaxies. We show that line
emission in reionization-era galaxies can be clumpy, extended, and spatially
offset from continuum emission, implying that galaxy assembly histories are
complex even at these early epochs. We publicly release fully reduced mosaics
and photometric catalogs for both the NIRCam primary and NIRISS parallel
fields.
