Proto Actor - Ultra fast distributed actors for Go, C# and Java/Kotlin
...Grain abstraction, which provides a straightforward approach to building distributed interactive applications, without the need to learn complex programming patterns for handling concurrency, fault tolerance, and resource management. This allows Proto.Actor to leverage in-process performance for realtime stream processing.
Horizon is a realtime, open-source backend for JavaScript apps
...Building realtime apps now requires understanding and manually orchestrating multiple systems across the software stack, understanding distributed stream processing, and learning how to deploy and scale realtime systems. The learning curve is quite steep, and most of the initial work involves boilerplate code that is far removed from the primary task of building a realtime app.