"You can self-host Mattermost in a very straightforward fashion." There's a very long chasm between "You can get the software running, and have it respond on a

"You can self-host Mattermost in a very straightforward fashion." There's a very long chasm between "You can get the software running, and have it respond on a port to requests" and "Providing a mission critical service that your project relies on". The key word here is service. It is often drastically underestimated how much effort is required to have a service available, especially at any sort of scale. Free/Open Source software is irrelevant as soon as you are providing a service, because by design, the only people who have control over the service, are the service operators, and the only people who really know whats running in production are the people who deployed the code. Given that, the only choice a user has is whether or not to trust whomever is providing the service, regardless of whether or not the software they are running is free/open source, or proprietary/in house software.