Running 5.7.3 under Jaguar (OS 10.2) without any problems. It's fast and stable and a very powerful tool. Linnsoft is amazing in that they keep upgrading the product adding new features that users have requested about every two weeks. And they do this for three operating system platforms. There is a discussion group on Yahoo dedicated to RT users and the programmers and technical support folks post there daily. I've never seen such excellent customer support in any software package.