Formal Concept Analysis (FCA) and its extensions have shown their e cacy and relevance in various application domains. We recently conducted a set of experiments using Relational Concept Analysis and FCA in the domain of agro-ecology. This motivated the development of a library named FCA4J, which includes Java implementation of algorithms to build structures and implications and to manage data, in particular relational context families. This paper presents the main features of FCA4J, its ecosystem, and a few use cases.