I know my fellow blogger wrote one post about this category before, and I felt an urge to continue writing about the subject. Yes, I know there is some work to be done when it comes to games in GNU/Linux, both support for proprietary games that can be played in Windows and also when it comes to free software. These games should work on both Windows and Gnu/Linux, if not directly it should work after compiling in an IDE.
So, say you like Minecraft but would like a free (as in freedom) alternative? There are some options:
A game that provides more advanced features than Minecraft server, as said in their website. It includes scripting and “griefing preventation [sic]“. It is written in Java and is licensed under the BSD License.
These three options is not the only options out there, but is a handful of them all. You could search on Google or Duckduckgo for more alternatives to Minecraft.
I would also like to add some games that I think my friend could also have mentioned; 0 A.D. and Unknown Horizons.
0 A.D. is a game written by Wildfire Games and contributors. It feels kind of Empire Earth, I think because you have different civilisations that can evolve two times if they have enough resources. It is licensed under the GPL. It is still alpha software, and sometimes a bit slow when playing, but still a good game with a lot of potential in my opinion.
Formerly named “OpenAnno” and is a free/open source Anno-like game. The game is under active development and a bit slow during gameplay, but this game has also a lot of potential, I think.
Finally, I would like to say that there is a free IDE for .NET languages, such as C#, called MonoDevelop. With this tool developers can port apps written in Visual Studio to Gnu/Linux.