Just make a online Markdown notebook using Firebase, build for personal use.
It's convenient to set up a comment system in Jekyll site with external social comment systems like Disqus or Duoshuo (多说). However, as you all know, Disqus was blocked in China and Duoshuo is going to shutdown. It's the time to rethink about the comment system (although I didn't get too many comments →_→), simple and controllable. And it becomes true with Firebase database.
Markdown makes writing blog posts simple and fast, but sometimes that simplicity comes with limitations. Recently on updating this blog theme, I'm intend to include images in the post with captions, and there wasn’t a straightforward way using Markdown. While adding an img tag is very easy with Markdown, I would have to do some fiddling to inset the caption.
Jekyll features a simple “Related posts” variable per post page with "site.related_posts", which contains the 10 most recent posts in default. However, it only works perfectly when LSI (latent semantic indexing) option was enabled. The Liquid tags might be helpful here.