GitHub is the online platform which offers distributed version control and source code management functionality for developers. There are Public and Private repositories available on it. Public repository will be accessible for all while private repository will be accessible to you and your team (with whom you share it).
A private repository was costing $7 per month previously, but yesterday Microsoft made an announcement which will be helpful for small team developers. If your team have three collaborators or less you can create unlimited private repositories for FREE.
From GitHub blog
GitHub Free now includes unlimited private repositories. For the first time, developers can use GitHub for their private projects with up to three collaborators per repository for free.
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FREE Alternatives to GitHub
BitBucket was the Free previous alternative to GitHub which offers Free unlimited private repositories with up to 5 collaborators (Still it allow 2 additional collaborators compared to the GitHub). Another Free alternative is GitLab which supports Unlimited private projects and collaborators have a limitation of 2,000 CI pipeline minutes per group per month on our shared runners .