RayDream saves in / exports to all major formats. By the way, if you just want to open rds files (one wonders why or how you do have rds-files at hand, but no copy of RayDream, but that's probably perfectly explainable) you could go for the end-of-life offer for Carrara 1.1 eovia has on their site. But as a lot of program-specific formats (quiz question: which program saves .t3d files?) are not stored with information other apps can handle. If this really is a problem, and you can't find someone around with RDS or Carrara, contact me, maybe I can do some translations on a rainy tuesday afternoon and send them by email (or on cd).