There were many other 3D transparency viewers and slide formats manufactured between 1930 and 1970. Many people have put up web pages describing their favorites. However, there have been several viewers of historical interest that seem to have been overlooked (at least from searches on the internet), so this page is an effort to give some of these orphans a little exposure to collectors and sellers.
This is a work in progress, and the pages that are not underlined are still under construction.