As far as socializing, Lemmy is pretty much the big one nowadays.
Well, a little Facebook too, to stay in touch with friends and family, but I use F. B. Purity to remove ads and other features I don’t use on Facebook (gaming, marketplace, reels/stories, etc.), plus an extension in Firefox to block Facebook/Instagram from snooping on my other browser tabs. Don’t want them building a profile on my browsing habits to customize ads for me, or to sell to third parties.
I also use Discord with my wife and a few close friends, so we can arrange an online video gaming night once or twice a week, and stay in touch the rest of the time.
Before Lemmy, I used Reddit a ton. Before that, I was a moderator for a forum called CommGuys.net (formerly 3C0X1.net), which was a forum for Air Force service members in the IT career field. The former site URL was our Air Force specialty code that designated the generic IT career field, but it changed in 2009, splitting into several different codes for different specialties, so they changed the site to CommGuys; short for Communications Guys, which is what they used to call IT professionals in the Air Force. Nowadays, they call them Cyber Guys, because we’re more cyber/web focused and less communications specific. But when social media sites were officially unblocked from Air Force computer networks in 2010, military people ran over to Reddit and Facebook and our forums practically died out, so the site owner finally shut it down.
Oh, and to officially date myself, my first social media platform was MySpace, which I didn’t even get involved in until after I left home and joined the military. Social media was not a thing in my childhood, and most of my childhood was without Internet. It didn’t become popular/commonplace until my preteen years, and content was sparse for many years after that. I did use AOL Instant Messenger (AIM), MSN Messenger, ICQ, and a couple others in my teen years, but that was basically direct messaging with friends through the Internet before everyone had cell phones.
Even as a teen/young adult, IRC was more of an “old nerdy IT guy” hangout spot, so I rarely got involved with it, despite joining the IT profession in the military. I expected it to die out as more advanced web functionality approached, but I guess some people really like the classics, and it’s surprisingly still a thing today.
Oh, and 4chan was a great site back in its early days, but then too many young kids started joining it and taking the “free speech” jokes seriously, so now it’s become a breeding ground for fascist misogynistic alt-right extremists. We used to joke around about that stuff, testing the mods to see what our censor limits were, since 4chan liked to advertise itself as the only place on the Internet where you could speak your mind without being silenced or banned. And, well… some people really pushed those boundaries to the extreme and eventually turned the site into a cesspool.