Vavr core is a functional library for Java 8+. It helps to reduce the amount of code and to increase the robustness. A first step towards functional programming is to start thinking in immutable values. Vavr provides immutable collections and the necessary functions and control structures to operate on these values. The results are beautiful and just work.
There are several additional modules that group around Vavr's core. All of these are supported by the Vavr open source organization.