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.
The Android app works well. I rarely have issues with it, except when switching back and forth between the web player and and the app, when it sometimes doesn’t properly sync progress fast enough.