Flex:- BlazeDS and LCDS

We all know that Flex is developing an RIA(Rich Internet Application) application.
This flex code should be integrated with the server side code. i.e. java or php etc.
Using BlazeDS and LCDS, java and flex code can be integrated.
BlazeDS is an open source where as LCDS is costly one.
 
BlazeDS is a web application and a program that handles the all communication between java and flex application

BlazeDS enables
Invocation of remote java from a Flex application.
Translate the java objects returned from a server to corresponding ActionScript objects and vice versa.
Manages the communication channels and connection types between flex and java.
and etc.