PyXPlot

set xlabel "$x$"
set ylabel "$y$"
set xrange [-pi*0.4:pi*0.4]
set yrange [-pi*0.4:pi*0.4]
set xformat "%s$\pi$"%(x/pi)
set yformat "%s$\pi$"%(y/pi)
set xtics 0.2*pi ; set mxtics 0.05*pi
set ytics 0.2*pi ; set mytics 0.05*pi
set trange [-5:5]
set samples 1000
set key below
set size square
set grid
set title 'The Cornu Spiral'
plot parametric (int_dq(sin(q**2),0,t)):(int_dq(cos(q**2),0,t))

Notes

The Cornu spiral.