GitHub is now the main source for GamePanelX project files, until real releases start going out again.
Master is the main Web Control Panel. You can get away with just using this to host gameservers. If you will be hosting servers for other people, need FTP Accounts for your users, and/or better security (Linux privilege separation etc), setup the Remote package after you setup the master (they work together).
Note: If you don’t know how to use Git, you can press “Download ZIP” on the bottom right of the GitHub page, and it will let you download the full release.