gedcom4j is an open-source, free-to-use Java library for reading (parsing) and writing genealogy data.
Most genealogy programs and tools can import and export their data to file in the GEDCOM file format. Using gedcom4j, you can write a Java program to load data from a GEDCOM file into a Java data structure for your examination and manipulation, and you can also save GEDCOM files out from the same data model, including data you created without having read a file first.
Please note that gedcom4j is not an application. It is a library (jar file) that can read, manipulate, and write genealogy data using the GEDCOM format in your own Java programs...including commercial, closed-source projects.
These details are provided for information only. No information here is legal advice and should not be used as such.