Want a lean Slack alternative? Use IRC. Want a fancy Slack alternative? Use Matrix.
Want a lean Slack alternative? Use IRC. Want a fancy Slack alternative? Use Matrix.
I want rich messages, images, links.
I want threads.
Anyone has usable threads yet? For the life of me I can't follow Slack threads.
Given that we're talking about search-engine-visible logs - just use an existing, public server.
> I want my messages to be synced between multiple devices including mobile ones.
I actually believe it's better for people _not_ to have Slack on their mobile, so as not to be pestered, but if that's what you want, then you want the "fancy" alternative. Matrix clients can offer you that.
> I want rich messages, images, links.
So, Matrix.
> I want threads.
If that's the case, maybe what you really want is a Discourse web-forum rather than Slack.
See discussion 7 years ago on serverfault.com, and the links therein:
How to set up a IRC server that logs all messages? https://serverfault.com/q/190069/113898
How to Offer Searchable IRC logs? https://serverfault.com/q/36886/113898
The bot option should be valid for Matrix as well, although there I'm not sure the bot world is well-enough developed to be 100% sure that a bot exist for every common desire like saving channel logs.
It's not too pretty though, but definitely usable: https://view.matrix.org/room/!SzcRUxcpYurpoctOzk:matrix.org