General Non-Markovian structure of Gaussian Master and Stochastic Schr\"odinger Equations

General open quantum systems display memory features, their master equations are non-Markovian. We show that the subclass of Gaussian non-Markovian open system dynamics is tractable in a depth similar to the Markovian class. The structure of master equations exhibits a transparent generalization of the Lindblad structure. We find and parametrize the class of stochastic Schr\"odinger equations that unravel a given master equation, such class was before known for Markovian systems only. We show that particular non-Markovian unravellings known in the literature are special cases of our class.