You can host the data and/or the app that can be accessed cross-platform. If you’re on someone else’s PC be it linux, windows or mac you can pop open a browser and visit a url to access your app with the stored data. Or you could host the data and access it using the clients on multiple/different systems.
what low-maintenance are you referring to? I have a server at home running proxmox and a container for docker. It hosts a website (caddy), website comments system (cusdis), sync, calendar, mail, mqtt, gps tracking, note taking, at one point i had home assistant but i dont have enough IoT to make use of it so i just stopped it. I check on stuff like once a month or maybe two months.
I have a domain on cloudflare to map internal IPs/services and use wireguard to reach the network. Tried Tailscale and Zerotier, there was a problem on some devices when switching from wifi to internet which was breaking internet access, switched to Wireguard and now i’m happy.