And for those not familiar with early Twitter, the hashtag was not a feature of the platform, but a shorthand way to indicate a topic. This of course was recognized and formalized by Twitter soon after, but I find it fascinating that it was a feature essentially developed by the users and more simply recognized by the platform later.

99 Percent Invisible did a whole show on this a while back: https://99percentinvisible.org/episode/octothorpe/

> a shorthand way to indicate a topic

And I imagine it was also inspired by IRC channels.

100% slack is essentially evolved irc.

The part I quoted was about Twitter, not Slack. Slack's relation to IRC was already mentioned. Essentially, my comment was "Not just Slack, Twitter too was inspired by IRC."

I'd bet that quite a lot of early Twitter users were also IRC users.