Beta software is fully developed and internally tested software. Since no company can possibly have all the hardware and software combinations of its customers, beta is the process of testing software for configurations not covered by internal testing.
We are offering beta Rendr to a limited number of people depending upon their Blu-ray player and PC models. We encourage everyone to sign up for beta and we will send you the beta version if and when we need testing with your specific configuration.
We benefit by finding problems with the software early. You get fully functional and fully supported software for free. Best of all, the software will update free of cost to the released version (and all future updates) automatically.