I know that there is a way to draw a spiral using the Bezigon tool, but it's complicated and take some time. What about add a spiral on the shape section? In inkscape, for example, you can fastly create a spiral, resize at the same time that you are creating the shape, add the number of turns, divergence and inner radius. You can also add a fill color to it. It's really simple and fast to create exactly what you want.
It would be useful because you can use spirals as watermarks on projects, and also, spirals are important on illustrations and logo designs for example.
Mostly I use Linux, but I have to use Windows sometimes and Inkscape is not that good on Windows. Gravit is running way too better and beautiful on Windows machines and that's why I'm migrating. Thank you, Gravit development team, you're doing a great job