@antenna
You may or may not be aware of JRiver's development model for these different platforms. The vast majority of the code for all platforms (Windows, Linux, Mac) are THE SAME. They have abstracted most of the platform specific stuff (window drawing, audio handling, etc) so that the same code can be used on all platforms.
There are still some things that are different about each platform, but as I understand it, it's not all that much. So, new builds come out for each platform whenever the person that compiles that version decides to compile it.
The key point here is that none of the non-windows platforms are "separate". Nor are they "ports" of the windows code. The code is (largely) exactly the same. Therefore they are actually developing all the platforms simultaneously through a single code base.
For me this is EXTREMELY impressive. Applause for the JRiver development team!!
Brian.