pods

The Pods Framework is a Content Development Framework for WordPress - It lets you create and extend content types that can be used for any project. Add fields of various types we've built in, or add your own with custom inputs, you have total control. Maintained by pods-framework on GitHub, where it has earned 1,121 stars from the community.

It's actively developed around wordpress-plugin, php, wordpress, and is a solid reference for anyone building with these tools.