GitHub repository: rgoldberg/picocli
Primary language: Java
Description: Picocli is a modern framework for building powerful, user-friendly, GraalVM-enabled command line apps with ease. It supports colors, autocompletion, subcommands, and more.  In 1 source file so apps can include as source & avoid adding a dependency. Written in Java, usable from Groovy, Kotlin, Scala, etc.