Rewire is a technology that was developed by Propellerhead Soft SE, the makers of Reason. The purpose of the technology was to create a connection between Reason and other DAWs; at the time, Reason was just a cool synth rack, and not a daw like it is today.
Rewire has become an industry standard technology. Its not just a way to connect Reason to a DAW anymore, its a way to connect a ton of different softwares... People use it all the time.. I use it all the time. I do not have a single completed Sonar project that does not make use of Rewire...