Wow, making a multiplayer game is really a challange, respect for you. Visual style make me to recall "liero", and I fall in nostalgic mood =). I'm check it out in the evening for sure.
Application complains about missing libs, It's a shame for us. I've updated game page - added archive with missing libraries.
To answer the question - Yes, we make it from scratch in C (only, without C++) using SDL2 library. At the beginning not the one of two of us have a C skill =).
You said about several sleepless days - I wonder how many people working on the game and how many hours in total it took? In comparison, there was the two of us working about 2 hours in a day with some rare day offs and sleepless Friday and Sunday nights.