AEM exposes Restful endpoints via servlets. You can use the default SlingPostServlet or write your own servlets.
That is - you can write a Sling Servlet that accepts GETs or POSTs. Other clients that are able to perform REST requests can sent REST requests to AEM by performing GET or POSTs. Here is an example of a .NET app interacting with AEM using the default SLingPOstServlet:
Of course - you can write your own Sling Servlets - as talked about here.