Home Assistant. This is open source home automation. It's great for managing your smart devices at home, focused on privacy as for example they have disabled remote access by default. Also they have a lot of things working out of the box, including for example the smart devices from IKEA (TRÅDFRI)

Jellyfin. This is an open source media server. Ideal for watching all your shows, movies, etc, all around your home network. It even has an open source mobile client at f-droid, or you can simply use the web interface.

Nextcloud. This is an open source server for managing all your private data, such as photos, notes, etc. It is basically a great replacement for google photos as you can simply keep your photos in your own network and see them with a similar interface. It also offers many other features commonly found on services like google drive and others.