C++

I'm using GLUT to write C++ programs with graphical interfaces: http://www.opengl.org/resources/libraries/glut/
It's very easy and short to code with, and it runs on all platforms.
For example a simple GLUT program which creates a window and draws a triangle would look like this:

#include "GL/glut.h"

void Render()
{
	glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
	glBegin(GL_LINE_LOOP);
	glVertex3f(0,0,0);
	glVertex3f(0,1,0);
	glVertex3f(1,0,0);
	glEnd();
	glutSwapBuffers();
}

int main(int argc, char **argv)
{
	glutInitDisplayMode(GLUT_DEPTH|GLUT_DOUBLE|GLUT_RGBA);
	glutInitWindowPosition(100,100);
	glutInitWindowSize(640,480);
	glutCreateWindow("Window Title");
	glutDisplayFunc(Render);
	glutMainLoop();
	return 0;
}