Here are a few online services which offer graphing functionality:

  • Desmos (2D only)
  • Math3d—a bit rough around the edges, but works well once you figure out the quirks. From what I can tell it doesn't understand juxtaposition multiplication with variables, i.e. you need to write $\sin(n\cdot\theta)$ instead of $\sin(n\theta)$.
  1. Graph a torus with major radius $K$ and minor radius $k$.
  2. Graph a Möbius strip.