We have tools to "explore" the Cardano blockchain, which are useful when you know what you're looking for. We argue that there's a different, complementary use-case which is to "observe" the blockchain and react to particular event patterns.

Oura is a rust-native implementation of a pipeline that connects to the tip of a Cardano node through a combination of Ouroboros mini-protocol (using either a unix socket or tcp bearer), filters the events that match a particular pattern and then submits a succint, self-contained payload to pluggable observers called "sinks".