structRDFaL - http://struct.arghc.ca/
The awkwardly named structRDFaL theme is a Jekyll theme primarily concerned with structured data (apply your own style!) using RDFa Lite. SEO is actually a secondary concern, but since schema.org vocabularies were used, seo should follow.
Link to the repo - https://github.com/arghc/structRDFaL
Jekyll Dash
A dark theme for Jekyll, inspired by Dash UI for Atom. 
Open sourced Ultra - super fast jekyll theme (weighs under 2kb). Perfect for your personal website, blog and portfolio.
Key features
Github: https://github.com/ronv/ultra
Demo: https://ultra-jekyll.netlify.com/
Szimpla - https://szimpla-jekyll-theme.netlify.com/
Szimpla is a responsive jekyll theme for static blogs. It was build with simplicity in mind and is minimalistic.
Szimpla theme features:
Hey folks, I just released a brand new portfolio theme for designers and web developers!
Show off your best work with this beautiful, minimal and customizable portfolio theme made for designers and developers.
Made is the perfect Jekyll theme for designers, web developers and other creatives to build an awesome personal portfolio website.
View more details or check out the live demo
Name - https://ramendaily.com
Ramendaily blog or magazine theme for Jekyll.
The theme is listed as sell theme on themeforest. 
Colorie - Colourful single column blog and portfolio theme.
Colorful, minimal one-column portfolio/blog theme built for Jekyll. Perfect for your personal website, blog and portfolio.
Demo: https://colorie.netlify.com/
Source: https://github.com/ronv/colorie
Top Features
Bulma Clean Theme - https://www.csrhymes.com/bulma-clean-theme
It offers a range of page layouts, configuration options, fully responsive and built with the Bulma frontend framework. It’s available as a ruby gem and works with GitHub pages!
Churel - Responsive Modern Jekyll Blog Theme
Churel is a modern blog theme with a responsive layout and elegant styling. There have multiple home page, tag page, author page, category page layout. Pages and posts include basic SEO markup for better search ranking.
Link : https://themeix.com/product/churel-responsive-jekyll-modern-blog-theme/
Jekyll | Help Center - https://github.com/gustavoquinalha/jekyll-help-center-theme
Ghostly - http://www.jmlilly.net
A personal web site theme using Jekyll
Ghostly is a blog-enabled, text-centered Jekyll theme with a minimal aesthetic and fade transitions, intended to meet the needs of academic researchers. This theme comes equipped with a double blog, a lightbox, support for online commenting, and a skeleton site with a readily customizable style.
New theme open-sourced! Sidey is a simple and minimalistic Jekyll blogging theme.
Demo: https://sidey-jekyll.netlify.com/
Source code: https://github.com/ronv/sidey
Screenshot:
I created a minimal yet beautiful Jekyll Theme called Leaf. It’s a free blog theme.
And, this is my first theme. I mainly created it to learn how to create Jekyll themes.
Here’s a screenshot.
I shared the story of this theme on dev.to:
dev.to/supunkavinda/i-created-a-jekyll-theme-in-375-minutes-eoj
(Link is removed because I can add only 2 links )
Friday Theme - https://sfreytag.github.io/friday-theme/
Friday Theme is a theme for Jekyll using Bootstrap 4.4 designed to build a great personal web site with a portfolio, blog and project documentation. It is compatible with GitHub Pages. It supports all the Bootstrap components, it has blogs with tags, it has syntax highlighting and it has SVG icons. It is customisable with SCSS by simply changing the default Boostrap variables.
One interesting thing: I built this theme to also teach myself Jekyll, which now powers my personal homepage. I decided to release the theme for other people to use.
Link to the repo - https://github.com/sfreytag/friday-theme
Academic Website - https://sylvaingchassang.github.io/academic_website/
A simple academic website that centralizes co-author management.
Repo: https://github.com/sylvaingchassang/academic_website
Jekyll Klisé - https://klise.now.sh
Klisé is a minimalist Jekyll theme for running a personal site or blog, light & dark mode support.
Source Repo - https://github.com/piharpi/jekyll-klise
Supply - https://supply.templates.supply
Supply is an e-commerce theme built with Jekyll and Tachyons CSS, with Gumroad integration.
Source repo - https://github.com/YJPL/Supply
