You're right that the general consensus is to take this time to vacation, relax, play video games, etc. Not study. You're also not the first person to try and study before residency starts. If that's what you want to do, you're not going to melt, but you might feel...overprepared? Realize, though, that plenty of people have gone through residency without any pre-residency preparation and have done fine.
To answer your question though: I remember using onlinemeded during med school and it was an incredible resource. Felt a bit similar to Pathoma in terms of usefulness. It looks like their intern program is only 8.3 hours which isn't that long, and it's free so it's pretty low risk. When I looked at this before I started, I realized the focus was more on internal medicine than ER content, but still stuff that you should know before you practice on your own.
Another good resource is EMBasic. He has a podcast you can listen to as well as a pdf/.doc file of the major EM chief complaints and workups. It's great to go over, but it definitely sticks more when you're actually applying what you learn to patient care.