Here are a few I like:

• Jellyfin - a media server software that allows you to organize and stream your personal media collection.
• NextCloud - a self-hosted file sync and sharing platform. Not as good as Google Drive (of course), but it can do the job.
• Bitwarden (with a Rust-written alternative named [vaultwarden] (https://github.com/dani-garcia/vaultwarden)) - a password manager for storing and autofilling login credentials.
• Matrix - an open network for secure, decentralized communication. WhatsApp, but in the Fediverse.
• PiHole - a DNS sinkhole that blocks ads and other unwanted content.
• Mycroft - an open-source voice assistant. You can make your own Google Home with it.
• OctoPrint - web interface that allows you to control 3D printers. Pretty handy if you have one!
• Gitea - a lightweight self-hostable GitHub
• Home Assistant - an open-source home automation platform. Can integrate a lot of other things in your house.
• The X-arr initiative - a collection of tools for managing and organizing media libraries. Pretty good if you deploy your own media server:
  • Sonarr - Select TV shows and it will automatically download episodes for you.
  • Radarr -> movies
  • Lidarr -> music