com.typesafe.akka:akka-contrib_2.12.0-M4 (maven):  This subproject provides a home to modules contributed by external developers which may or may not move into the officially supported code base over time. A module in this subproject doesn't have to obey the rule of staying binary compatible between minor releases. Breaking API changes may be introduced in minor releases without notice as we refine and simplify based on your feedback. A module may be dropped in any release without prior deprecation. The Lightbend subscription does not cover support for these modules. 
Keywords: actor-model|akka|cloud-native|concurrency|distributed-actors|distributed-systems|hacktoberfest|high-performance|reactive|streaming