EventStoreDB
The stream database optimised for event sourcing
...It was built from the ground up for Event Sourcing, we believe that makes it the best solution in the market for building event-sourced systems. Event Sourcing offers some great benefits over state-oriented systems; the key ones are explained below. An event-sourced system stores your data as a series of immutable events over time, providing one of the strongest audit log options available. All state changes are kept, so it is possible to move systems backward and forwards in time which is extremely valuable for debugging and “what if” analysis.