  Non-Markovian master equations describe general open quantum systems when no
approximation is made. We provide the exact closed master equation for the
class of Gaussian, completely positive, trace preserving, non-Markovian
dynamics. This very general result allows to investigate a vast variety of
physical systems. We show that the master equation for non-Markovian quantum
Brownian motion is a particular case of our general result. Furthermore, we
derive the master equation unraveled by a non-Markovian, dissipative stochastic
Schr\"odinger equation, paving the way for the analysis of dissipative
non-Markovian collapse models.
