The REST API is targeted at building custom Web applications, mobile apps, and HTML interfaces that use or display assets from Assets Server. Of course it can also be used for server-side languages such as PHP, .NET and Java / JSP.
All the previews provided by Assets Server are based on Web standards and can be used in Web browsers or on any Web-enabled mobile device.
Note: The Assets Server REST API does not always respect all of the official REST guidelines. When it diverts, it is always in the interest of making the API easier to use from HTML based Web browsers and Flash, Flex and AIR applications.