I just logged in for the first time in over 25 years a few weeks ago. I found https://web.icq.com/ which does not require an email address: only the ID and password. And back then I used a single password for everything.

And it worked! All my old online friends from my childhood were there, my profile message, etc. While most were offline, a few showed up as online and I quickly messaged them!

But my excitement died down as no one responded. Were their accounts hijacked? Is that status invalid? I have no idea. But I was disappointed. It's still cool the service is up all this time.