Strapi is an open source Headless CMS written in Node.JS. The software is still in Beta. It’s not really ready for prime time. It works, sure, but it has bugs. I would not recommend it for something large yet. At the time of writing they are on version 3.0.0 Beta 18.7. Strapi helps in building out an API, that you can use to feed data to your app, or website. For example, you can create specific pieces of you database through the admin, however, there is not frontend. That is because it is headless.
You can use Vue.js alone with VuePress and have a super fast website. If you need more dynamic content, for example, comments, Strapi is great for the backend. Using them together allows for a fast website experience. Definitely worth looking into if you are a developer.