Today we've (finally!) added Amazon Web Services (AWS) to Review Signal. AWS is one of the largest cloud hosting providers and power many other web hosting companies that are built on top of them (such as Heroku).
It took so long to add AWS because it's been very difficult to figure out what it is. AWS provides so many different products and tools that it's difficult to just call it a hosting company. They provide infrastructure for many of the core components of anything on the web - much of which is beyond what most people consider web hosting. They are an Infrastructure-as-a-Service (IaaS) provider that very few companies rival in terms of capability and scale (the only other one that jumps to mind is RackSpace).