I think there's an argument to link to both. Since the OSS version was posted I think it's good to note the author's updated version even if it's no longer OSS. Looks like they want 30€/yr, which is far from extortionate if it's a good tool.
To be clear, in the description on Internet Archive page all this info exists, including active link to "new official site" and a link to Wikipedia article, I've wrote, where all the story of rattleCAD development has been described in details.