| Interface | Description | 
|---|---|
| MessageStream<M> | A stream of messages that can be transformed into another  MessageStream. | 
| OutputStream<M> | An output stream to send messages to. | 
| Scheduler<K> | Allows scheduling  ScheduledFunctioncallbacks to be invoked later. | 
| Class | Description | 
|---|---|
| KV<K,V> | A key and value pair. |