Frames may be obsolete but they still seem to be well-supported: MDN.
One problem with frames is that search engines sometimes dump you in a frame, with no navigation or indication that the page is incomplete. For example I got here via a search on part of that page. (Admittedly it was not the first hit.) It also changes the URL at the top.
By clicking on the User Name, you will requery the forum for that user. You will see everything that he or she has posted with that Mudcat name.
By clicking on the Thread Name, you will be sent to the Forum on that thread as if you selected it from the main Mudcat Forum page.
By clicking on the Subject, you will also go to the thread as if you selected it from the original Forum page, but also go directly to that particular message.
By clicking on the Date (Posted), you will dig out every message posted that day.
sj