Equinox is an F# library for event-sourced systems, providing a consistent abstraction over multiple stream-based storage backends including CosmosDB, DynamoDB, EventStoreDB, MessageDB, SqlStreamStore, and an in-memory store. In production, it enables applications to define domain logic as pure decision functions that produce events, while the library manages optimistic concurrency, caching, snapshots, and retries. The core is the `Decider` pattern: an aggregate loaded from a stream, a decide function that returns events, and a fold that applies events to produce new state. Access strategies (e.g., `LatestKnownEvent`, `RollingSnapshots`, `Custom`) control how state is reconstructed from stored events, trading read cost for write cost. The architecture is modular: the `Equinox` package defines the core interfaces (`ICategory`, `IStream`, `Decider`), while separate NuGet packages implement storage adapters. The library is used as a dependency in larger applications; sample projects (`Store/Domain`, `TodoBackend`, `Tutorial`) demonstrate its use. Key entry points include the `Decider` class for command/query execution, `Category` for resolving streams, and store-specific connectors (e.g., `CosmosStoreConnector`, `DynamoStoreConnector`). A CLI tool (`Equinox.Tool`) provides provisioning, benchmarking, and data inspection commands across all stores. External dependencies are minimal per package: `Equinox` depends only on `FsCodec` for serialization; store adapters require their respective SDKs (Azure.Cosmos, AWSSDK.DynamoDBv2, EventStore.Client, Npgsql, etc.). The library includes comprehensive caching (`Equinox.Cache` wrapping `System.Runtime.Caching.MemoryCache`), metrics via Prometheus, and a load testing harness. Despite some deprecated adapters (legacy EventStore TCP, SqlStreamStore) and high complexity from multiple backends, the core patterns are clean, well-tested, and production-proven at Jet.com.