I needed to make some plots of parametric equations and found a very capable and handy free tool: Winplot. Here is Wikipedia article about it: and the official website. It has a wide variety of graphs that it can plot including graphs based on differential equations and graphs using polar coordinates. Very handy if you just want to graph something without having to learn a massive software system. Here are some very helpful videos to get you going. About 10 minutes of viewing is enough to begin using it on your own.