I've been using Rust to process fairly large amounts of streaming financial data. I am using Protocol Buffers (and evaluating Cap'n Proto) for network serialization and Kafka for buffering/queuing, and overall the library support is quite good.

Previously I was using JVM languages for this purpose, but grew weary of the resource footprint, and especially the unpredictable GC pauses. I am aware of the Azul JVM which removes GC pauses and of various Java techniques to avoid GC altogether, but switching to Rust provided a GC-less model from the ground-up, a powerful type system, and familiar functional programming facilities at no cost.