Whether you want to automatically sync your photos or audio recordings from your phone directly to your desktop PC, or to sync your notes between all your devices, free and open source Syncthing will help you do this securely, privately, and reliably. I’ll show how I’m doing this, and how I’m also keeping older versions of changes my notes so that I can restore them if needed (a bit like a basic backup).
Unlike many backup or sync applications, Syncthing will sync any number of folders directly between your devices, so no server is required. This can be done without even knowing the IP addresses of the devices. It can also sync over the Internet to a friend, if you want to share backup space with each other – you can set your own encryption password for each folder to keep your data private.