  We consider Roche lobe overflow (RLO) from a low-mass star on a nearly
circular orbit, onto a supermassive black hole (SMBH). If mass transfer is
unstable, its rate accelerates in a runaway process, resulting in highly
super-Eddington mass accretion rates, accompanied by an optically-thick outflow
emanating from the SMBH vicinity. This produces a week-month long, bright
optical/Ultraviolet flare, accompanied by a year-decade long X-ray precursor
and post-cursor emitted from the accretion flow onto the SMBH. Such ``Circular
Tidal Disruption Events (TDEs)" represent a new class of nuclear transients,
occurring at up to $1-10\%$ of the canonical parabolic tidal disruption event
rate. Near breakup rotation and strong tidal deformation of the star prior to
disruption could lead to strong magnetic fields, making circular-TDEs possible
progenitors of jetted TDEs. Outflows prior to the final stellar disruption
produce a circum-nuclear environment (CNM) with $\sim \rm 10^{-2} \, M_\odot$
at distances of $\sim 0.01-0.1 \, \rm pc$, likely leading to bright radio
emission, and also similar to the CNM inferred for jetted TDEs. We discuss
broader connections between circular TDEs and other recently identified classes
of transients associated with galactic nuclei, such as repeating-TDEs and
Quasi-Periodic X-ray Eruptions, as well as possible connections to luminous
fast blue optical transients such as AT2018cow. We also discuss observational
signatures of the analogous RLO of a white dwarf around an intermediate mass
BH, which may be a multi-messenger source in the LISA era.
