This is a library inspired by OpenFeign. It removes the need to write any concrete implementations of guzzle clients and instead allows you to annotate an interface with the functionality you want. It is then auto generated for you so you do not have to write a single line of code for your HTTP client implementations.
This has the benefits of abstracting away the guzzle version from you since the code is handled for you and you just have to define an interface. It reduces the boiler plate code you have to write in order to get your clients implemented. And it's always cool to have the ability to just read documentation for your interfaces and have a complete outline as to what your clients do.
There is documentation covering building your clients with the annotations using the client builder. You can find the documentation here.