Mostly writing realtime distributed systems/platforms, usually streaming and processing data to organise them into places where other subsystems and people can easily consume and find meaning in it. Have also worked-on/built realtime data aggregation, anomaly detection, alerting, streaming platform, etc., as well as things like task schedulers which can execute tasks at predefined time/event taking decisions in runtime as to which task to run next. This resulted in the easier deployment of batch processing pipelines and jobs, and easier maintenance in case of typical failover scenarios. Lately working on distributed tracing (https://expediadotcom.github.io/haystack/).