Zep

Memory infrastructure for agents. Instead of stuffing a conversation back into the prompt, Zep builds a temporal knowledge graph per user — facts with validity windows, so the graph knows not just what is true but when it stopped being true — and serves the relevant slice back as context. Ingests chat, documents, events and business data, not just the conversation in front of it. They call the whole thing a Context Lake, run it inside customers' own VPCs, and maintain Graphiti as the open-source graph framework underneath (30K+ GitHub stars, their figure).