Stratum is an open-source, log-structured storage engine built in C++ that stores hierarchical data — documents, input chains, and output chains — with O(1) lookup via an in-memory hash index. All writes are append-only to segment files on disk, with a background compaction thread that automatically merges and garbage-collects old data. It exposes a gRPC API so any language (Python, Go, Node, Java) can query it using auto-generated clients from a single .proto file. Run it as a Docker container and connect to it from any external project in minutes.