In short, data streaming is getting popular. Apache Flink, Apache Spark, ksqlDB are traditional players. They work well in some cases, but have challenges on easy-to-use, easy-to-deploy, on even performance sometimes
Proton, RisingWave, Materialize, etc are the alternatives. In the end, it's always 'case by case' to pick up the best tools working for your team in your projects.
If you think this is too general, well - Materialize no longer provide the latest code as an open-source software that you can download and try. It turned from a single binary design to cloud-only micro-service - RisingWave has been open-sourced for 1.5 years and released their cloud mid of last year. It builds its own row-based historical storage, while Proton leverages ClickHouse for faster OLAP-like workload. Also there are more SQL functions supported in Proton, because it's powered by ClickHouse. Proton uses local SSD as the main storage and has an option to send older data to object storage. While RisingWave primarily uses object storage, and use local disk as cache. So in general Proton can achieve lower latency for both streaming or historical queries.
I am a big fan of coffee and drink different kinds of coffee over time, even on the same day. It's all about the use cases and preferences. This could be applied to choose open-source tools to query live data. In the last Current conference, me and Gang had a talk about different tools and different coffee. You may check https://www.timeplus.com/post/query-kafka-with-sql-current23