I've added a few missing features to Tribe- Timers and Futures.
Timers provide a way to tell an actor to do something in the future. Tribe supports both one-shot and periodic timers so I believe all the major usage patterns are covered. Adding this feature was fairly easy since all of the low level details are hidden in my Workers gem.
Futures make it easy for an actor to ask another actor to perform an operation and return the result. Previously you would have to use custom events and a lot of boilerplate code to accomplish this. Both synchronous (blocking) and asynchronous (non-blocking) futures are supported. More information on both types can be found in the readme file.