ZTF's high-cadence data stream will enable new investigations in a wide variety of fields.  The ZTF survey will average more than 300 epoch each year over the entire Northern sky, giving nearly four times the number of exposures of SDSS Stripe 82 over 100 times the sky area.  Public access to the ZTF data will provide a wide variety of community science, much unanticipated.  We describe a few selected highlights below.

Young Supernovae

Prompt detection and rapid spectroscopic followup of supernovae within the first day of explosion is key to answering major questions about their progenitors and environments. Early observations of thermonuclear supernovae (Type Ia) can constrain the progenitor radius and distinguish single- and double-degenerate origins. Rapid spectroscopy of core collapse supernovae identifies progenitor signatures in the flash-excited CSM. ZTF's wide-field camera will enable it to find a young supernovae less than 24 hours after its explosion during each night of observations.

Fast / Rare Transients

ZTF's wide area, high cadence survey will identify relativistic transients that decline rapidly in a few hours. The PTF surveys have identified the first GRB optical afterglow discovered in a blind search as well as a fast-declining event which may be the first of a class of baryon-loaded "dirty fireballs." ZTF will discover a few to tens of these events each year.

ZTF will also search for electromagnetic counterparts to the first gravitational wave detections from advanced interferometers. The precise localization and observational constraints provided by a counterpart association will be vital to understanding the physics of the gravitational wave progenitor system. Our PTF-proven pipelines will sort efficiently through the thousands of progenitor candidates, while ZTF's all-sky variability catalog will efficiently cull foreground variables and transients.

Galactic Plane Variables

Time-domain observations in the Galactic Plane will enable a wide variety of stellar science. New crowded-field photometry pipelines currently being tested in iPTF will allow ZTF to conduct the most extensive variability survey of the Galactic Plane to date, with over 300 visits each year over the entire Northern Plane. These data will reveal outbursts from young stars, trace the star formation history of the Milky Way with variable stars, constrain the M dwarf flare rate, and enable gyro-chronology of young K dwarfs.

Active Galactic Nuclei

Frontier studies of supermassive black hole evolution, Large Scale Structure, and dark energy require massive samples of AGN for statistical study. Optical variability data improves the purity of these samples relative to use of color cuts alone. Coadds of ZTF data will provide this information over a wide sky area, while high-cadence monitoring will probe the extremes of AGN variability.