Texture Packer-Gui is, as the name states, a GUI for the awesome texture packer that comes with every libgdx distribution.
The application can also be used through command-line, if you need to include texture packing in your build workflow.
If you don't want to use project files, you can directly set the input and output directories, as well as defining a settings file.
The "--silent" option directly packs the given project or input folder without spawning the GUI. Else, the GUI is spawned with input, output and settings set according to what was given.