WSRP(Web Services for Remote Portlets): A OASIS-approved specification designed for communications with remote portlets. WSRP allows portals to display remotely-running portlets inside the portal pages without doing any additional programming. This means that the portlets can run on one server or container and the portal itself can run on another. Portal and portlet communicates with each other using SOAP-based Web Services standard. Due to WSRP portability, Java portal site can also communicate with .NET portlets as long as they communicate via WSRP and vice versa.
You can develop WSRP portlets using Oracle WebCenter framework, IBM portlet factory, Liferay portal, .NET Portlet Toolkit etc.
Why do you need WSRP? If Web services offer a mechanism to create platform-independent services, and JSR-168/268 defines a standard by which to develop portlets, why do you need WSRP? The answer is simple. While Web services give you the ability to reuse back-end services, WSRP lets you reuse the entire user interface!