I currently have to get a game project done for an application.
The request was that the app can be run without problems on Windows and MacOS.
Well, I never did anything for Mac before and don't even have one available...
Can you give me some directions what I should look out for?
Also are there emulators of some kind to test my project in a MacOS environment?
Unfortunately, your best option is to either find someone with a Mac and compile it there or use OS X within a Virtual PC.
If your source isn't using any Windows APIs then it should theoretically port without too much hassle.