LiquidText recently introduced a Windows version of their product.
I don’t know what “compatible with zettlekasten” means, since Zettlekasten is just a way of taking notes and keeping a running index. I do not recommend either LiquidText or MarginNote as the place where you would maintain a Zettelkasten collection of notes – both apps are designed for annotation and note taking using a PDF as the basis.
Neither app exports directly in markdown format. In both cases you need to do some intermediate step to get notes out of MarginNote or LiquidText and into an Obsidian vault or other destination. Doable, in each case, but moderately cumbersome.