[barrrrald]

GitLab is a really interesting example, but I don't know if it'd have positioned itself as an "open source alternative"

As for Mattermost, RocketChat, and Outline – I think these are great examples of projects positioned this way that haven't broken out. They all seem great, but it's not clear that being an "open source alternative" to Slack really worked for Mattermost...

[willsmith72]

i know of some gigantic companies using self-hosted mattermost for data privacy reasons. perhaps they have less marketing incentive, but i would certainly call that a success

[tommoor]

> I don't know if it'd have positioned itself as an "open source alternative"

It was literally a pixel for pixel open source clone of GitHub for the first few years.