In terms of most used for me, it would be:

• Nextcloud: contains my contacts, calendar, and photos synced with my phone, as well as access to files on my server from any web browser.
• Home assistant: both automated and remote control of your lights, thermostat, etc.
• Audiobookshelf: only really useful if you have an audiobook collection
• Vault Warden: self-hosted bitwarden. Not really all that important to self-host, since a bit warden’s clients are open source.
• Frigate: only useful if you have security cameras.
• Navidrome: only useful if you have a music collection.
• Jellyfin: only useful if you have a movie / TV collection.