Brewology

Okay, I've been out of the loop of things for a while. Last time I checked, PSX ISOs could be converted to an EBOOT with this one program, but I can't seem to be able to track that program down anymore. Then I hear all this talk about Popsloader, and I have a question:

What the heck is that? Does it let the PSP run the ISOs without conversion? And does it work on 3.90? Where can I get it?