RIA is a way to create an RICH-type interface that can be created using stadardise technologies such as (x) HTML, CSS and JavaScript and using embedded technologies such as Adobe Flash and Microsoft Siverlight. RIA usually runs inside a web browser and usually does not require client-side software to work. Most RIAs run their client parts in a special isolated area of the client’s desktop called the sandbox. The sandbox limits the visibility and access to the file and the operating system on the client to the application server on the other side of the connection. This approach allows the client system to process local actions, calculations, reformatting, etc., thereby reducing the number and frequency of client-server traffic, especially compared to client-server implementations built on so-called thin clients. One distinguishing feature of RIA (unlike other web applications) is its client engine, which mediates between the user and the application server. The client engine loads when RIA starts. The engine can be supplemented during the subsequent operation with additional downloads, in which the engine acts as a browser extension for processing the user interface and communication with the server. Read more ..
A single page application is a thin client. This is a perfectly normal web application. The interface is built in HTML5, CSS3 and JavaScript. There are many open source open source frameworks whose goal is to provide the best solution for single page applications. SPA also aims to provide a better user interface with less frequent communication between client and server. SPA is suitable for desktop applications, but it can be used to create good mobile websites or hybrid applications. Additional Information.