One of the creators of Hydro here. Yeah, one way to think about Hydro is bringing the dataflow/query optimization/distributed execution ideas from databases and data science to programming distributed systems. We are focused on executing latency-critical longrunning services in this way though rather than individual queries. The kinds of things we have implemented in Hydro include a key-value store and the Paxos protocol, but these compile down to dataflow just like a Spark or SQL query does!