Uber was on Hipchat, briefly experimented with Slack, went back to Hipchat, and then moved to our own Inhouse chat based on open source project, starting around the beginning the year.

It was bad the first few months, but except for a recently publicized utterly embarrassing security vulnerability, in the last 2 months it's been working great. The mobile app is now much, much better than the HipChat ever was.

What project is the internal tool based on? Mattermost?

Yes, the internal tool is called uChat and it's based on Mattermost but Uber heavily contributed to Mattermost to make it scale. More details here: https://eng.uber.com/uchat/

I personally can do UI of Slack client in 5-8 months (so 5-8 man/months) + one/two backend developers needed. And it will be almost native client with client distribution less than 5mb.

As a proof, it took me 2 months to make this application: https://notes.sciter.com/ (and site for it in that time too).

That's the easy part. The hard part is scaling, marketing, and building a business/platform around the product so that you take it worldwide.

Several people have built Slack clones and there's even multiple open source projects out there. Building a company and business at a scale like Slack is the incredibly difficult part and nobody has managed to replicate that.

That's true. My personal educated estimation is that only 5-10% of income is spent on R&D in established companies.

I'd pay for an alternative "lite" Slack client for basic channels, DMs, and attachments. With 10+ accounts, my 2017 mac struggles under the weight of the Electron mac client

A competitive app would have:

- easy signup for public access

- integrations for killer apps in other verticals

- plugin architecture

- public and private apis

- mobile app(s) with 80% of core desktop functionality

- end-to-end encryption

Maybe it's sufficient to extend IRC. Add support for custom emojis & Giphy integration.

Voice, video conferencing and screenshare would be essential.

I've participated in design of application similar to that (it is already on the market): voice, video, camera desktop sharing and textual chat. First version was made in 9..11 months: core UI team - 3 developers for desktop. 2 developers for mobile clients, one for each platform. Server side 3-5 as it supports video transmission for 1000 and more participants. Platforms: Windows, Mac OS, Linux, Android and iOS. Small, manageable and so effective professional team.

Ask Discord.