What are some alternatives?
When comparing twitter.github.io Kestrel and Amazon SQS, you can also consider the following products
nginx - A high performance free open source web server powering busiest sites on the Internet.
Apache Kafka - Apache Kafka is an open-source message broker project developed by the Apache Software Foundation written in Scala.
CloudAMQP - CloudAMQP automates every part of setup, running and scaling of RabbitMQ clusters. Available on all major cloud and application platforms.
RabbitMQ - RabbitMQ is an open source message broker software.
IBM MQ - IBM MQ is messaging middleware that simplifies and accelerates the integration of diverse applications and data across multiple platforms.
IronMQ - IronMQ is the distributed systems together by providing a reliable way to communicate between services and components.