Slack definitely started from the software niche, but is far from the only player in the field.
Others mentioned Mattermost, Discord, but really, there are so many viable options out there. See this list of 25+ alternatives for example: https://fleep.io/blog/best-slack-alternatives/
From cloud-based to self-hosted, open-source and commercial... As long as they integrate with the tools devs use, there will be devs who use it.
Imagine, there's an app with Slack's functionality that already has such interop with email as you've built here :) Fleep: https://fleep.io/
Anyone who does not want the group chat experience can be included in conversations via email.
Currently, that does mean getting all messages via email, and not @mentions (nice idea, worth considering for Fleep's product team). But idea is similar:
Full disclosure: I do work at marketing in Fleep :)
It's not a messaging protocol - email was never built for conversations, which is why conversations over email often get clunky, confusing and finding some piece of information later is near-impossible.
The thing is, most 'email killers' like Slack are closed systems and thus have no shot at replacing email - the reason why email has persevered is its openness, how it is the lowest common denominator in online communications (ahem, 2,5bn users worldwide).
Instead of a new open protocol, Fleep (https://fleep.io) has built a messenger that relies on the email protocol by integrating with email seamlessly. With Fleep, you can send messages to anyone who has an email address - if they're not a Fleep user yet, they will receive the messages as normal emails. As a Fleep user, however, you already get the improved conversational experience of emails.
(Full disclosure: I do work at Fleep and I absolutely love the product, the ambition and the ingenious approach our founding team has taken to merging IM & email.)
Microsoft didn't force that, they reflected it. Microsoft just made their software facilitate what users actually wanted to do. They don't care about all that tedious effort to scroll and selectively trim and indent and format quotes for a neatly curated conversation. They just want to start typing. They just want all that junk out of their way. Microsoft merely reduced resistance to what users were already finding natural to do.
Email was built as a digital version of snail mail. I guess good old mail services are conversations in a way - but both snail mail and email are more for sharing information than having a written conversation.
Sort of like - I'll send this piece of information out, and maybe I'll get something in response. Maybe I won't.
In fact, Slack users have reported an average of 50% reduction of internal email (source: https://slack.com/results). But you're right, Slack is a closed system, and thus it cannot really replace email when used for external communications.
This is where Fleep comes in - a messenger that works with email, too. You can include anyone in a conversation with their email address, and if they're not a Fleep user yet, they can participate in the conversation via email. Fleep: https://fleep.io/
(Disclaimer: I do work at Fleep, and I love it :) )
Hadn't heard of Fleep before, but thought immediately that it might solve one use case for me.
After checking the pricing (good), if there was a self-hosted version (no, but maybe not a deal breaker) I looked for the Android app installer. Only available from Google Play Store. Unfortunately, that kills Fleep for me.
Please consider making your app directly downloadable and not reliant on Google Play Services.
I don't have Goggle Play Services installed on my phone and am not going to do so.
I understand why companies want their apps in the "Store" for discovery purposes. However, I don't understand why they won't provide an alternative direct download.
I do have F-Droid installed, but I appreciate companies may not want to open source their app. No problem, but I also won't be forced to install Google Play just to obtain it.
The Google Play store is also not accessible in China, an no doubt a few other countries, so it's just sensible to provide an alternative download anyway...
