Git is a free and open source distributed version control system designed to handle everything from small to very large projects with speed and efficiency.
Git Repositories can be self hosted on your own server, or hosted on one of several public hosting / collaboration platforms:
GitHub is the largest and most popular Git Hosting provider in the world. They offer repositories for open source as well a private reposiroties for individuals, small teams, or enterprise customers. GitHub was acquired by Microsoft in 2018.
GitHub offers native Continuous Integration workflows using GitHub Actions.
GitHub Pages offers static asset hosting directly out of a GitHub Repository.
GitHub is my favorite Git Host and nearly all of my coding projects are hosted there.
GitLab is a large Git Hosting provider. GitLab is free for open source repos.
GitLab comes with a CI/CD offering called GitLab CI.
GitLab offers many options for orgainizing teams, companies, repositories, projects, etc.
Atlassian also provides Jira (ticket tracking software), Confluence (colaborative Wiki), and Trello (task management) products for software teams. Understandably Bitbucket comes with excellent integrations with these products out of the box.
Bitbucket provides their own CI/CD solution.