Tailscale: easily allows for setting up a mesh VPN network, completely unbothered by firewals and NAT. Sometimes I fix stuff on my homeserver from my phone with Termux.
Tachiyomi: great manga reader, I only hope that sync gets officialy built in (I’m already using SyncYomi).
Revolution IRC: IRC client.
Nextcloud: backs up photos on my homeserver instead of Google Photos. Sadly uses a lot of battery, probably because I have around 50K images to scan.
Jellyfin: streams shows and films from my homeserver.
There’s so many: