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(nθ)\sin(n\cdot\theta) instead of sin(nθ).\sin(n\theta).
  1. Graph a torus with major radius KK and minor radius k.k.
  2. Graph a Möbius strip.