A prolly tree is similar to a B+ tree, but its node boundaries are determined by the data rather than by insertion order. Each node is addressed by the hash of its contents, and updates create a new root while sharing unchanged nodes with older versions.

This makes it useful when an application needs more than basic key/value storage: cheap snapshots, efficient diffs, three-way merges, deduplication, and incremental sync between replicas.

Some use cases I’m exploring include local-first applications, versioned database indexes, Git-like filesystem snapshots, agent memory and event logs, and reproducible RAG indexes where the exact data snapshot used for an answer can be recorded.

It’s a storage primitive rather than a complete database. The goal is to provide the ordered-map layer and let applications choose their own storage backend, data model, and conflict policy.

The project is still evolving, and I’d appreciate feedback—especially about real-world use cases, the API, and what is missing.