A standard for communication between in-cab trucking apps.
For high-level information about OpenCab, see https://opencabstandard.org.
For the latest stable interface docs covering the currently-defined providers and data, see https://docs.opencabstandard.org/.
See org/opencabstandard/provider/ for the actual interface files defining the key constants used for communicating information between apps.
HOSContract and IdentityContract are boilerplate classes you can use if you prefer not to define your own string constants, and AbstractHOSProvider and AbstractIdentityProvider are abstract classes you can subclass to make provider implementation even easier. Both are provided as-is and you aren't required to use them—you can absolutely implement the provider interface by subclassing ContentProvider directly on your own.
See OpenCabProvider/ for an example of a collaborating application that provides identity and HOS information to a consuming workflow application.