Jekyll is a Ruby static site/blog generator created by GitHub for GitHub pages .Jekyll allows to create a fully fledged blog using only static files,you don't need anything like database or PHP all you have to do is install Ruby and Jekyll ,choose a template which suits your needs and then start your blog and guess what you can benefit from a high quality hosting for free using GitHub pages so you don't need cheap low quality hosting or otherwise high price hosting .You can use Jekyll instead of WordPress for starting your blog with all the benefits of WordPress .
If you remember your first computer course about computer storage then you probably remember that before databases people were using flat files to store data but for the sake of many reasons such as data access speed,security etc.. they've created databases so what Jekyll did is going back to use files for storing data.
Recently i'v discovered another great way for using Jekyll .Since i build websites and web applications for clients and for my own personal use,the kind of websites that require heavy database access or api endpoints .Providing an initial prototype is requested by many clients ,Jekyll allowed me to prototype quickly without the need for database access with the features it has such as frontend matter,YAML,pages ,data files and collections so i can build a static website and simulate database data using collections and data files .
Jekyll also allows me to quickly test new ideas for my personal projects so i don't have to build a database or server backend before i make sure the idea is realizable.
Jekyll compiles your sass files automatically and generates you css files so you don't need any other system to compile your sass .