Yes, Arroyo is an alternative to KSQL, although more in the design-space of Flink.

KSQL is pretty simple and easy to run if you already have Kafka, but will be much more expensive and harder to scale due to its reliance on Kafka streams for persistence and shuffling of data in processing DAG.

And with Confluent's embrace of Flink in the past year (https://www.confluent.io/blog/cloud-kafka-meets-cloud-flink-...) it's not clear that KSQL has much of a future.

If you look at the page, I guess the answer is yes. Or more precisely, an alternative to Flink written in rust.