Flink is a strong competitor. Spark itself also claims to be a runner up with minibatching.

But streaming model is more widely adopted outside of frameworks. AWS Lambda or Fass platform can be viewed as streaming model with simple topology.

Flink is popular. I believe Samza also fills a similar niche.

There's also Kafka Streams which is suitable for many cases that do not warrant a full cluster with all the management and trouble required.