My personal experience with using Slack as just a in-company chat app has been fine. I enjoy using Slack more than Teams or Discord.
All their integrations kinda suck though, and its not uncommon for integrations to randomly break with no discernible changes elsewhere.
We used to have a local devs slack and any time someone came up with a random slash command one guy would add a new php script to power that command. I assume a lot of it is just an abandoned API that nobody cares about anymore because Microsoft forced Teams into Office so it took over corporate America in waves. I cant remember the last place I worked at that didnt just use Teams.
Speaking of php slack was built with php until they followed Facebook with Hack (which is essentially a modern flavor of php)
I hate how Slack has no syntax highlighting for code blocks. Even Discord has it.