As of April 14, 2020, GitHub is free for both public AND private repositories. There is no limit on the number of repositories or the size of teams (collaborators) that can access private repositories for free.

Advanced features require using a paid plan. There are four tiers named "Free", "Team", "Enterprise", and "GitHub One". These are summarized at https://github.com/pricing.

Actions use "hosted runners to automate your software development workflows. Write tasks and combine them to build, test, and deploy any code project on GitHub. Minutes are free for public repositories." If minutes in a month are exhausted, more can be purchased ala carte. It is not necessary to upgrade to the next tier.

Packages are used to "host your own software packages or use them as dependencies in other projects. Both private and public hosting available. Packages are free for public repositories." For JavaScript, this is an alternative to npm.

Required reviewers enables configuring repositories to "ensure that pull requests have a specific number of approving reviews before collaborators can make changes to a protected branch" such as merging.

Code owners enables configuring repositories to "automatically request reviews or require approval by selected contributors when changes are made to sections of code that they own."

SAML single sign-on uses "an identity provider to manage the identities of GitHub users and applications."

Advanced auditing provides an audit log that can be used to "quickly review the actions performed by members of your organization."

Community-powered security allows building "safer code faster with automated code scanning and suggested fixes from top security researchers".

Actionable metrics allows users to "set goals, track key performance indicators, and accelerate innovation with insights validated by the GitHub community."

Continuous learning allows teams to "create custom courses and help your team level up their skills on the same platform they code."