I've been making a set of local- and files-first iOS apps for myself - Photo Gallery, Music and Contacts.
I use Linux on my computer and an iPhone and wasn't happy having to use a cloud to sync my data between my devices. Syncthing/Synctrain + my apps allow me to keep everything on my private network, without ever touching a server or having to self-host something like Immich.
Same, but for android. My best one so far is my own launcher/home screen. Works great.