Much on the old forum, though as it’s search capability is limited to the thread titles at the moment I’m not sure it’s easy to find (hopefully not too long before that changes). Also any links between threads won’t work as they related to the forum as it was live.
REW is a great tool, is free of charge (donations invited), just needs a measuring microphone. I use a Behringer ECM8000, but easier I think would be the one that REW recommend as I think it includes a USB interface.
It can show the room response at different positions, also distortion levels, and decay information etc. The data can be interpreted to diagnose a variety of room or speaker issues, including things like the contribution of early reflections.
I used REW to assist finding best speaker and listening positions in a problematic room, and also to set up my active crossover including phase correction, I also used it to set up DSP taming of some peaks in response when I use my speakers in a non-ideal position part of the time (a capability of my active crossover).
Also, some room treatment suppliers, the one I know is GK acoustics, can interpret REW data to advise on best room treatment should you go down that line.
Another person who I know has familiarity with it, and may be more knowlegeable that I, is @Xanthe.