As an adult, I used Google Sheets as a group chat among my friends. We had different employers with different internet restrictions. Before that we used a self-hosted Telnet chat server, until someone's employer blocked that.

It was a lot more fun than Discord, Slack, or any other dedicated chat client. With Sheets, we'd do fun little gags and bits in the spreadsheets. Everything ended up being really personalized and owned by us. Now we just send boring messages on WhatsApp. I miss the old ways.