Wisper is a micro library providing Ruby objects with Publish-Subscribe
capabilities.

It supports:
- Decouple core business logic from external concerns in Hexagonal style
  architectures.
- Use as an alternative to ActiveRecord callbacks and Observers in Rails apps.
- Connect objects based on context without permanence.
- Publish events synchronously or asynchronously.

WWW: https://github.com/krisleech/wisper