Kafka is a high-throughput, distributed messaging system originally developed at LinkedIn to manage the service's activity stream (data about a Website's usage) and operational data processing pipeline (about the performance of server components).
Kafka is effective for processing large volumes of streaming data -- a key issue in many big data computing environments. Storm, developed by Twitter, is another stream-processing technology that's catching on.
The Apache Software Foundation has taken Kafka on as an open-source project. No jokes about buggy software, please ...