The Overviewer GUI is an unofficial GUI for the Minecraft Overviewer, a CLI based map renderer for the Java edition of Minecraft.
This tool allows you to simply specify a world directory and an output directory, and optionally some render modes to use on that world. For more advanced users, it also allows you to specify a config file.
It can also manage your installation of the Overviewer for you, or you can point the application to an existing installation.