Codespaces
Codespaces is VS Code on the web. It can be launched directly from a GitHub repo to edit and commit code in that repo. It supports running and debugging web applications. VS Code extensions can be configured. It supports an integrated terminal for executing shell commands.
This is currently in beta (as of 5/13/20), but early access can be requested at https://github.com/features/codespaces.
There may be features that are not free.
Discussions
“Discussions” provides a way to host a forum associated with a repository. This is a better place to ask and answer questions about a repository than creating issues. It can also be used to announce work in progress and new releases.
This is currently in beta (as of 5/13/20) and only selected repositories have been allowed to use it. It is expected that all repositories will have the ability to add a discussion forum in summer 2020 by enabling the feature in Settings.
Security
A new tab labeled “Security” in the web UI of GitHub repos reports “common vulnerabilities and coding errors”. These are listed in three categories, “Security advisories”, “Dependency alerts”, and “Code scanning alerts” (in beta as of 5/13/20).
In addition to identifying potential issues, it explains why the issues matter and provides suggestions on how to resolve them.