This applet requires the Java package to run: GetJava Download Button

Some examples:

point([1,2])
triangle([1,2],[3,4],[5,6])
triangle([1,2],[3,4],[5,6],red)
triangle([1,2],[3,4],[5,6],green,filled)
quad([1,1],[1,10],[10,10],[10,1])
a=[1,1]
b=[20,1]
c=[20,10]
d=[10,15]
e=[1,10]
S=shape(a,b,c,d,e)
translate(S,[10,10])
rotate(S,[20,20],90)
reflect(S,[10,10],[20,20])
you can have as many lines as you wish, points are specified by two number in square brackets [3,4].