Obsidian is a note-taking software. It is not open source.
What is an Obsidian Vault?
Obsidian calls the folder you keep your journals, your notes, your settings and your plugins an Obsidian Vault.
Obsidian has a paid service for synchronizing your vault called Obsidian Sync. But since all your data is stored in Markdown files, you can also use something like Syncthing.
Using Obsidian with Jekyll
Some people wrote about their workflows using Obsidian to publish a Jekyll website. Below are some examples.
I have a small Jekyll plugin that parses Markdown files from my Obsidian Vault and publishes them on my website.
Obsidian supports plugins to extend the functionality of the application. These plugins are easy to install, you can just put the manifest and JS files into your Obsidian folder and when you sync your files your plugins get sync-ed as well.