GitLab is an opinionated and integrated set of tools based on convention over configuration that offers a superior user experience. It provides features like continuous integration, static site generation, issue tracking, code review and more. The document encourages using GitLab.com for free private repositories or self-hosting. Contributing to GitLab's open source project is also presented as a way to get feedback, build your resume and potentially get a job there. The architecture follows an MVC pattern with services and finders to power its functionality.