Nessie is a shared context layer that auto-syncs AI conversations across major providers such as ChatGPT, Claude, Gemini, Perplexity and Codex into a queryable, structured knowledge base accessible to both humans and agents. The platform preserves reasoning and decision-making context so thinking compounds over time rather than starting fresh with each session, turning scattered AI conversations and documents into a shareable, owned AI brain. Nessie is based in the San Francisco Bay Area and is part of Y Combinator's Fall 2025 batch.