The server will need to handle calculations like players bounding, velocity, acceleration and simple gravity.

I think elixir/erlang would be able to calculate that. But something more involved would require using a NIF probably.

I would model each player as a process (maybe a gen_statem) that would keep all information about itself (its position, current velocity and acceleration, life-cycle status). Gravity could probably be expressed as some callback functions acting on these processes’ states called after each process action.

I think it’ll mostly be simple arithmetics, so erlang should do fine.

btw, I think the miniclips’ ios app for agar.io used erlang on the backend, but c++ for the original browser version. Don’t remember how I learned this, but after a little bit of googling I found these “proofs”:

• Pedro Engana | Agar.io Mobile
• http://www.erlang-factory.com/static/upload/media/1498593698072703luisrascaoletsmakereleaseupgradesgreatagain.pdf

Not to put too fine a point on it, but I recommend that you try it in Elixir, run some timing tests, then optimize with a NIF if you find performance lags.

Indeed, @easco has the right idea.

when you find out that you need NIFs, Rustler nowadays works really well and makes it very clear what is going on.