Well, game might not be the best term, but here we are. If its any clue I think it was distributed through itch. 

This little social game was pitched as the players being AIs leaving messages for each other as the huge Machine-City around them died. Players would receive little prompts, which they would respond to by recording little messages and sending them into the Twitter tag cloud until they finally got their death notice and their signal died. 

I'm almost certain I didn't dream this. 

Anyobe remember it? 

Try to look in here itch.io/library/things-to-rate. Maybe it's there?

There's a similar game called Sad Robot,  but it's more explicitly about observing the end of humanity. https://blue-golem-games.itch.io/sad-robot