...and because so few people apparently realise that's Slack's value is in the quality execution, which can be copied by a decent team (but takes a phenomenal team to beat).

As far as I can tell Gitter is owning the space for open source projects, so there are definitely niches here.

Yeah, I expect there are, maybe Gitter can leverage their OSS adoption to their advantage. I don't know their product or approach well enough to comment.

I don't find slack to be particularly well executed. It's often obvious that I'm dealing with a (poorly executed, laggy) html UI.

It's segfaulted in JavaScriptCore on my machine. So apparently they've managed to combine the performance of HTML with all the security of C++.

Their success seems to be mostly a matter of not being as enterprisey as hipchat and being less geeky than IRC.

Genuine question: what did/do they execute on so well? I've only read about them having a great launch strategy.

In my view; product design & build quality. Yammer were already doing most of what Slack does. Tiny Speck took that and UX'd the shit out of it until it was a joy to use.

Gotcha, it's the first corporate chat app I've used outside of Skype, so I guess I don't know how bad it was, ha. I've personally had trouble with how unintuitive Slack's UI can be sometimes, when it seems like they're just trying to find places for all their features. But it's gotten ridiculously better in their last redesign.