AWS open-sourced a language called Cedar that enables users to easily create and enforce access control policies. 

It provides a unified framework for policy creation and management across multiple clouds, simplifies policy writing, and supports popular authorization models such as role-based and attribute-based access control. Additionally, AWS has adopted a verification-guided development process to ensure the security and safety of Cedar.

The open-sourcing of the project also includes the Cedar language specification and SDK which offers libraries for authoring and validating policies and authorizing access requests. 

Amazon Verified Permissions uses Cedar to allow you to manage fine-grained permissions in your custom applications. With Amazon Verified Permissions, you can store Cedar policies centrally, have low latency with millisecond processing, and audit permissions across different applications. 

The open-source libraries of Cedar allow users to test and validate policies on their own computers before deploying them with Amazon Verified Permissions. This makes it possible to use Cedar to run applications not connected to the network, allowing users to customize the libraries to meet their needs.

Additional details on the project are available here