Hi, @Susan @All worked on all those who commented on an answer (in chat, no). At least in the StackOverflow site. @Caleb Do you knows something about this feature?

@PaulVargas No, @all does not work for anything on Stack Overflow comments or anywhere else. The only thing it would possibly do is ping a user who's name happened to start with "all".

@Caleb OK. Thanks! Some time ago, I received a notification and saw @All. But I do not remember the details.

@PaulVargas You were probably either the owner of the message being commented under (it always pings this person no matter the @ conditions) or the last person that commenter successfully pinged and their comment had no recognized username pings (it re-pings the last user in some cases).