Syncthing is free, open source software that can be used to easily synchronize an Obsidian vault between your computer and phone/tablet. Not only free, but completely secure, private, and blazing fast. Here are links to an article I wrote explaining how to use it.
- Biscotty’s Workshop not mobile friendly :-(
- Substack
- Medium.com
There are many ways. Git based solutions, or any repo based solutions,don’t give instantaneous synchronization though.