GravitySim is a gravity simulator (duh) written in C, using the Barnes-Hut algorithm to approximate gravity interactions between objects. The only dependency is the GLFW2 library, you shoud be able to install it using either apt-get on linux or homebrew on OSX.
Installing GLFW2 on OSX
brew tap homebrew/versions brew install --build-bottle --static glfw2
make mac for OSX or
make linux for linux (only tested on ubuntu). Now you should be able to run it using
To customize simulation you can call it with different arguments.
./gravitysim number_of_galaxies objects_per_galaxy galaxy_size
./gravitysim 10 1000 100 creates 10 galaxies with 1000 objects per galaxy and diameter 100 pixels.
./gravitysim 10000 1 1 creates 10000 galaxies with one object per galaxy and diameter 1 pixel.
You could also customize a lot of options using build_config.h file (such as G constant, sd treshold, max speed or max mass), but it requires rebuilding whole project. Have fun.