We use:
* Matrix / Synapse for comms (slack alternative) (managed hosting through etke.cc)
* OpenProject for project management (linear alternative) (deployed on VPS so we can shim their premium token check)
* Kimai for time tracking and invoice generating (VPS)
* Crater for financial tracking (VPS)
* Outline for wiki (we tried bookstack and it was just too weird) (VPS)
* Vaultwarden for password management ("managed" hosting through elestio)
* EspoCRM for CRM and as a CMS for marketing sites for our members (VPS)
* Coolify as a PaaS (heroku / vercel alternative) (VPS) <- my favorite recent addition, lets any member just chuck projects up with whatever resources they need super easily, for "free" (we have a fatass VPS we got on sale from racknerd)
* Cal.com for meeting invites (vps)
* Baserow for basic cms (airtable alternative) (vps)
* docuseal for document signing (docusign alternative) (vps)
We usually deploy via docker containers and manage all our various VPS and containers with portainer.
I have a member that keeps pestering us to self-host emails as well but google already has us by the shorthairs with us on Migadu: clients often tell us our emails go to spam. Not much we can do about it we have like 50 email handles and no budget (yet) to give google the new price per email they're charging.