Mildly reminds me how being online on AIM or ICQ was an actual invitation to chat. I had so many interesting conversations with people I barely knew. There's no source of that signal that someone is open to chitchat these days, and it's in my opinion kind of killed what was once great about online communication.
Would anyone still use a desktop-only (no mobile) messenger where you have to run/turn on intentionally (not always-on like most mobile-first messengers nowadays), lists online/offline friends the way AIM/ICQ did, and you can only send messages with online friends? I get that most leisure computing has moved off of desktop to mobile in modern days, but there's definitely enough of us nerds who're on a computer a lot…
I do wonder, though, if there’s a gap for a messenger app that runs only while in the foreground in your phone [edit: or tablet or computer!] - or maybe until you next lock the screen, so you can ‘be online’ only while reading, playing a game, or doomscrolling.