Well, MySpace for starters.

Facebook Marketplace seems to have totally replaced Craiglist as well, where I live, for buying/selling. Facebook Messenger took over e.g. MSN for a lot of people, the News Feed replaced a dedicated news site for a lot of people, and so forth. Events replaced Evite I think (or similar?), FB Photos basically replaced Flickr back in the day...

2 most recent - stories basically destroyed Snaps growth potential and Reels are on track to overshadow TikTok.

I don't see Reels being anywhere close to that. YouTube Shorts seems to be a more successful TikTok copy.

MySpace? Most of the other pre-Facebook social media sites too. It's not about being an exact copy, but sharing enough features that it can subsume those roles.

Snapchat

(I’d say that twitter killed clubhouse also)

The all time classic would be Instagram copying Stories from Snapchat.

Marketplace? I miss when Craigslist used to be popular :(

Snapchat. Only schoolkids use it these days.