Experimental Ruby library by Ismael Celis for exploring event-sourcing patterns independently of the web. Core primitives are command and event data structs (commands are intent, events are past facts). A Decider class encapsulates the command lifecycle: a state block initialising state, evolve blocks updating state from each past event, and a command block that, given evolved state plus a new command, checks invariants and emits events. Reactions glue commands together — a reaction observes an event, performs side effects (e.g. calling Stripe) and dispatches the next command (e.g. ConfirmPayment). A Projector superclass consumes events and writes read-models to arbitrary stores (DB, file, Redis, Elasticsearch). Test helpers accept given/when/then specifications over any reactor. The Sourced runtime handles asynchronous distribution, per-partition claim locking (similar to Solid Queue), parallel replay with per-stream ordering, command-event correlation for full workflow tracing (request ID can seed the chain), time-travel state inspection, and a web dashboard to stop/restart/replay reactors and rebuild projections by resetting offsets. Newer versions use Dynamic Consistency Boundaries — events carry attributes and are queried to build virtual streams for each decision rather than being tied to one stream. Prism-based static analysis emits workflow diagrams. Ismael has used Postgres and now SQLite as the store, chosen to simplify dependencies while focusing on patterns.