Having tried OGP (Open Game Panel), Game CP, Game Panel X and TC Admin. I will give some pros cons.
OGP - Pro Free Linux/WindowsCon - designed for Linux setup though with a lot of effort I did get the Windows Version Running on Windows Server 2008. I then found the game xml files were not easy to setup and had trouble getting Window only Games to run. If you are good with linux and have lots of spare time great as FREE and worked well on some games but quite complex to use.
Game CP - Pro Super Simple SetupCon Expensive when the trial finishes and game setups limited. Nice GUI but not as advanced as TC-Admin.
Game Panel X - Pro Linux easy install Con No longer supported limited game files and limited setup options.
TC Admin - Pro Windows/Linux - The one most company's use reasonable documentation Useful Forum. Game Files often available from Forum. Reasonable Integration to Billing Software.Con Expensive (Game CP about the same.) Documentation is somewhat limited. Having used it for about 18months I would say read it! Then look at the supplied game xml files and see how they use MODS Variables Steam etc to then configure your own.
I just saw a new FREE panel Space CP looks free for 1 Server may be worth A try. I bought TC Admin as the FULL Licence works out cheaper in the long run.
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