Hey Guest! Ever feel like entering a Game Jam, but the time limit is always too much pressure? We get it... You lead a hectic life and dedicating 3 whole days to make a game just doesn't work for you! So, why not enter the GMC SLOW JAM? Take your time! Kick back and make your game over 4 months! Interested? Then just click here!
You can use languages other than GML to write extensions, but only on platforms where the language in question is supported: C-family languages on Windows and Ubuntu, Objective C on Mac/iOS, Java on Android, JS on HTML5. In any case, the mainstay of every project is still in GML.
Like I said, if you're this hellbent on not using GML, then get something else that doesn't involve GML.