You can use the code from these repositories to experiment, test, build, create patches, issue pull requests, etc.
https://github.com/jakartaee/platform - Project repository hosted on GitHub.
https://github.com/eclipse-ee4j/jakartaee-tutorial - Project repository hosted on GitHub.
https://github.com/eclipse-ee4j/jakartaee-firstcup - Project repository hosted on GitHub.
https://github.com/eclipse-ee4j/jakartaee-firstcup-examples - Project repository hosted on GitHub.
https://github.com/jakartaee/jakartaee-schemas - Project repository hosted on GitHub.
https://github.com/jakartaee/jakartaee-api - Project repository hosted on GitHub.
https://github.com/eclipse-ee4j/jakartaee-release - Project repository hosted on GitHub.
https://github.com/eclipse-ee4j/jakartaee-renames - Project repository hosted on GitHub.
https://github.com/jakartaee/managed-beans - Project repository hosted on GitHub.