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Open source, Apache 2.0 licensed project of mine: CivicGraph. It is a Foxx Microservice for ArangoDB that features VCS-like semantics in many parts of its interface. It retains all changes that its data (vertices and edges) that have gone through to reach their current state. It supports point-in-time graph traversals, letting the user query any past state of the graph just as easily as the present. Its API is split into 3 top-level categories:Document create, replace, delete and update.