For personal reference and for the lazy (i think it's complete, did it in a hurry in a break):
- Notion & Google Docs Alternatives: Capacities, Fibery, Tana, Nuclino
- Zoom Alternatives: Whereby, Jitsi Meet, Senfcall, Vowel
- Slack Alternatives: Mattermost, Element (Matrix), Rocket.Chat
- Gmail & Google Calendar Alternatives: Proton Mail, Tutanota, Mailbox.org, Infomaniak
- Notes & Markdown Docs: Anytype, Obsidian, SiYuan
- Task & Project Management: Fibery, Nuclino
I note that a good portion of these are commercial products, frankly I'd trust MUCH more a FOSS product than a commercial one after so damn many over the years have betrayed us all in the search for profit, if you're gonna migrate to something you may as well go for the FOSS ones that are less in danger of enshittification (not a guarantee but far less of a chance since a fork kills all the walls around a walled garden pretty quickly), even if the FOSS product is not as polished.