Today, klausi pushed our first pre-alpha release: rules 8.x-3.0-unstable1:
First unstable pre-alpha release of Rules for Drupal 8. This is not usable at all at the moment and is only intended as developer preview. The code mostly consists of bare bones classes with quite a few unit tests, but there is not much functionality implemented yet.
Current state of the architecture:
* Using and extending Drupal core Action and Condition plugins
* Created an early Context and ContextDefinition system
* Organizes Rules components as RulesExpression plugins
* Implemented basic Rules component containers such as action sets, AND and OR condition sets, as well as a Rule class itself.
* PHPUnit tests and some integration tests.
You can find more information about further plans and achieved goals in the roadmap.