GameCP is described as ': game & voice server hosting control panel - create, manage and control game, voice or radio servers'. There are more than 10 alternatives to GameCP for a variety of platforms, including Linux, Self-Hosted solutions, Windows, the Web and Mac. The best alternative is Ajenti. It's not free, so if you're looking for a free alternative, you could try LinuxGSM or Pterodactyl. Other great apps like GameCP are Pufferpanel (Free, Open Source), Open Game Panel (Free, Open Source), WindowsGSM (Free, Open Source) and Crafty Controller (Free, Open Source).