Managing all those household docs: https://docs.paperless-ngx.com
Backups of mail accounts: https://www.offlineimap.org
Cloud storage for phones: http://nextcloud.com
Mirroring podcasts locally: https://github.com/akhilrex/podgrab
Managing dynamic service dns via plugins: https://coredns.io
My own matrix instance: https://matrix-org.github.io/dendrite/
Backups: https://restic.net
Media Management: https://jellyfin.org
Relay only tor help: https://www.torproject.org
S3 compatible storage: https://github.com/seaweedfs/seaweedfs
Git + CI: https://about.gitlab.com
Managing SSL and container proxying: https://traefik.io
Mirror the docker registry locally: https://github.com/docker-library/docs/tree/master/registry
Samba support for the windows hosts: https://github.com/ServerContainers/samba
HTTP/S Proxy with support for modifying results: http://www.privoxy.org
Database: https://www.postgresql.org
Datastore: https://redis.io
and a bunch of support software. Paperless has Tika and Gotenberg as deps for example.