It’s a fantastic software. All of your files are kept in plaintext, too, which is important to me.
You do NOT have to pay for syncing, you can pay them for their services, but I use syncthing to sync from my phone to my PC and server. It updates almost instantly. They also don’t try to block you from using third party sync options.
Obsidian is a notes software, but you can make canvases like this and link multiple notes together. It also supports mark down.