You are correct I made a typo. The actual requested page URL nevers ends with a slash so your code should work. Does this rewriterule cope with many folders deep? Could you please help an old guy liek me and explain (([^/]+/)*[^/.]+) so that I fully understand it.
If this then copes with all links both from inside the site and from outside the site. What code do I need and where do I place it to make sure that the 100's of existing outside links that are expecting to go to /emulators/index.php?folder=atari/800 will also still work, without getting caught in a loop?