> My personal opinion is that Slack has been so successful primarily because nothing older than it (IRC, Campfire, HipChat) was a decently modern product by the time Slack launched and Slack was really good at marketing.

I disagree about the decent competitors -- there is e.g. Flowdock which in many ways (such as proper threading) is still better than Slack, and was doubly so back then. I think it's more about access to VC money and network effects, and indeed the successful marketing you mentioned.

It's funny, we were early (?) adopters of Flowdock, back in about 2012, on one particular project. We used it fairly happily for a year or so, and then just sort of forgot all about it and drifted back to Skype (I think with a brief flirtation with Hipchat whilst we were doing something Atlassian-centric), probably because Skype was free and Flowdock wasn't. In around 2014 suddenly everybody started using Slack, and I found myself wondering how, really, it was much of an improvement over Flowdock and why it gained massive traction. (I suspect marketing and the fact that Slack is effectively free for many types of teams.)

Now that you mentioned it, Slack being free was probably a huge factor indeed. Flowdock should have adopted some kind of a free tier for tiny teams too to stay competitive.

Slack being free plus ease of use for non technical folks is why we adopted slack.

Flowdock is free for teams of 5 of less, and for teams comprised of students.

Flowdock was a more opinionated service and that was IMO to it's detriment. It's primary usage wasn't internal communication but rather communication around social media.

Slack took the simplicity of IRC and gave it a modern interface with things like showing a preview when you link. easily share files etc.

> It's primary usage wasn't internal communication but rather communication around social media.

What makes you think that? I don't see any connection between Flowdock and social media. As far as I can see, it's purely an internal communication tool with easy file sharing, hooks for external services as GitHub, and so on.

As far as I remember it started as that. But maybe that's not accurate. I just remember them pushing how twitter could be monitored and then important tweets could be send around the organization to deal with them.

That feature is a flow (or channel) specific "inbox". You can add different sources such as e-mail, GitHub pushes, CI results, or the Twitter you mentioned. Basically looks like an in-channel RSS feed of different sources. Personally I love the feature.

A neat thing is that you can start a discussion thread from any of these items, so the context of the discussion is clear.

Oh I like FlowDock a lot was just trying to explain how I believe Slack won over it by being less opinionated about how it approaches conversation. It's IRC core functionality and then apps on top for specific needs.

Flowdock went a little further ahead when it came to how they constructed the base communication.

Flowdock has great ambitions, but it was hard to wrap your head around it. Slack came in with an unapologetic focus on chat, which helped anchor it in people's minds. They certainly want to be and do more than chat, but using that frame of reference really helped them.

A little marketing feedback: could a screenshot or two be put on the main home page? Or is it still just early days on the project?

Leading is a stretch, I've seen way more Mattermost and Rocket.Chat installations these past few months.

Mattermost is OSish, but Rocket.Chat seems to be a much more modern/UX friendly version compared to Zulip and fits the bill with FOSS.