Elastic MapReduce - AWS big data platform using open source tools like Apache Spark and Hadoop. Like renting a supercomputer cluster specifically designed for processing massive datasets.
A genomics research company uses EMR to process DNA sequencing data that would take months on regular computers.
All provide managed big data processing with open-source engines (e.g., Spark, Hadoop). EMR/HDInsight/Dataproc are cluster-based managed services; OCI Data Flow is primarily serverless Spark (you submit jobs without managing clusters).