This looks useful as an additional Slack archive tool. I have no affiliation with the company. Ran into it after seeing Pulumi Slack starting to use it. https://www.linen.dev/

I'm signed up and will be talking to their founder this week. I don't see how they can comply with Slack's ToS legally and since they do also offer a paid version of Linen, I'm skeptical as to how extensive their free service can really be. I'll report back here when I know more.

Another thing to consider is the gdpr. People agree to join slack and have their messages here but I'm not sure that it's legal for the messages to be archived on a different service. People must somehow agree also for that

Indeed. I have scheduled a meeting with the CEO of Linen next Monday and have introduced myself as co-owner of this Slack and sent him a list of questions that will need to be answered -- including GDPR and CPRA concerns. I'll report back here next week.